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Easy Leftover Birthday Cake Rice Krispie Treats

Wondering what to do with leftover birthday cake? Make fun birthday cake Rice Krispies treats with cake crumbs, mini marshmallows, and sprinkles. Drizzle with white melting wafers to add some pizazz.

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Cutting board filled with leftover birthday cake Rice Krispies treats, cut and drizzled with white chocolate.

The presents are opened. The wrapping paper was disposed of. You’ve accepted your new age. But still, days later, the leftover birthday cake stares at you from the cake box.

Sure, it was great when the candles were blazing and the “happy birthdays” filled the air. But now? It just looks sad.

If you do not want to throw out a still edible cake, no problem. Enter a new dessert – leftover birthday cake Rice Krispies treats.

These Rice Krispies are made like the original treat, but they are more fun. They have chunks of cake and frosting mixed in with the cereal.

And if that isn’t enough, you will also find mini marshmallows and colorful jimmies hidden in there too. If you want to get really fancy, dip them in white chocolate and sprinkle more jimmies on.

Why You Will Keep Coming Back to This Recipe

Stack of 3 leftover birthday cake Rice Krispies treat on a dessert plate stack.
  • This treat recycles leftover birthday cake. No need to throw cake remains out. Instead, transform it into a totally unique treat.

    And it may be one of the best things to come out of your party. Cuz turning another year older isn’t one of them.
  • It is a fun dessert. Birthday cake Rice Krispies treats don’t look plain. They are permeated with colorful jimmies and delicious cake bits. Then they are decorated with white chocolate for an added splash.
  • Incredibly easy to make. Rice Krispies treats are always simple to throw together. Tossing in frosted cake crumbs adds about 10 seconds to the prep time, and it is well worth it.

Ingredients

Ingredients for leftover birthday cake Rice Krispies treats.
  • Butter and marshmallows. You will have the greatest success when you use Jet Puff marshmallows. Store-brand marshmallows are unpredictable. They often get hard too quickly.

    Try using mini marshmallows. They melt swiftly, and you will have your sticky sauce ready in no time. Buy here.
  • Rice Krispies cereal. You can use regular Rice Krispies cereal if you have leftover vanilla birthday cake. Buy here.

    However, if your leftover cake is chocolate, try making this recipe with Cocoa Krispies. Buy here.
  • Leftover birthday cake. No need to scrape off the frosting (unless there is a ton) for this recipe. Just crumble the cake remains and get ready to stir them in.
  • Sprinkles or jimmies. Add some color and decoration with sprinkles. Buy here.
  • White dipping chocolate. Melt some white chocolate into the treat. Then melt even more so you can drizzle chocolate on the cut bars. Or dip a few pieces in the chocolate. Either way, white chocolate adds some birthday magic to the recipe.

    Ghirardelli white melting wafers are the best. But almond bark can also work. I prefer either one of these over real white chocolate, which can be harder to work with.

You may also be interested in reading about white chocolate vs. almond bark. The article explains when it is best to use each one.

Substitutions

  • Swap out the Rice Krispies cereal for another type of dry cereal.
  • Use leftover cupcakes work instead of birthday cake. Cupcakes work just as well.

Variations

  • Instead of cake crumbs, crumble Oreo cookies or Hershey’s cookies and cream candy bar and add it to the mix.
  • Make the Rice Krispies with M&Ms, nuts, or toffee bits.

Directions

STEP 1: Prep the equipment and ingredients.

Greased quarter sheet pan for birthday cake Rice Krispies treats.
  • Coat a 9 X 11-inch Pyrex pan or a quarter sheet pan with shortening. Or spray it with nonstick spray.
  • Crumble leftover cake pieces. Make good-sized crumbs so they don’t get lost in the mixture. You can use cake with frosting if you would like.

    Making the crumbs ahead of time and storing them in the freezer before making this treat is an excellent idea.
Bowl of large cake crumbs.
  • Pour the Rice Krispies cereal, cake crumbs, and the reserved mini marshmallows into a large mixing bowl.

STEP 2: Make the marshmallow sauce.

Steps for making the marshmallow sauce for Krispie treats.
  • Melt the butter in a large pan on the stove over medium-low heat.
  • Add the marshmallows and stir until they are almost melted.
  • Sprinkle in the white chocolate melting wafers and stir until the sauce is melted and smooth.

STEP 3: Mix and press the treats into the sheet pan.

Steps showing mixing the dry ingredients into the marshmallow sauce for Rice Krispie treats.
  • Remove the pan from the heat and pour the sticky sauce into the bowl with the cereal, cake crumbs, and mini marshmallows. Stir to incorporate the dry ingredients into the sauce.
  • Add the jimmies and stir to combine.
  • Press the mixture into the greased pan. Wet your fingers under the kitchen faucet and shake off the excess water. Then use your fingers to lightly press the mixture into the pan, trying to get it as level as possible.

STEP 4: Dry and cut the squares.

Closeup of a quarter sheet pan filled with a recipe of birthday cake Rice Krispies treats.
  • Allow the Rice Krispies treats to dry for about an hour. Chilling it in the refrigerator can speed up the process.
  • When the Rice Krispies have set, cut them into squares.

STEP 5: Drizzle on white chocolate or dip the squares into the melted wafers.

Cutting board filled with leftover birthday cake Rice Krispies treats, cut and drizzled with white chocolate.
  • Melt the reserved white chocolate in the microwave until it is smooth. Scrape it into a zip-top baggie (or, better yet, use a decorating bag). Cut a small hole in one corner of the bag.
  • Drizzle the chocolate back and forth across the Krispies treat squares.
  • To dip the treats in the chocolate, heat the melting wafers in the microwave at 50% power for 30 seconds. Repeat in 15-second intervals until it is smooth. Dip half of a cut treat into the chocolate and shake off the excess.

    I usually dip some squares and drizzle others. It gives the serving plate some variety.
  • Sprinkle again with jimmies if desired. Give the white chocolate 5 minutes to dry.
  • Serve the treats right away.

Tasty Tips

  • Use fresh marshmallows. This is not the time to dig out a bag of old marshmallows from the back of your cabinet. If you do, getting them to melt smoothly will be frustrating. You risk overheating them, which leads to hard Krispies treats.
  • Use fresh white melting chocolate. If the chocolate has been in your pantry for a while, it may be hard to melt smoothly. You don’t want to have to wrestle with the marshmallow/chocolate mixture.
  • Use frozen cake crumbles. Crumble the cake and then keep it in the freezer before making the Rice Krispies. Frozen cake crumbs stay together better when being mixed in the sauce.
  • Use low heat and be patient. Making Rice Krispies treats on the stove over low heat (instead of using the microwave) is a surefire way to prevent overheating and hard treats.
  • Get your fingertips damp before pressing the mixture into the pan. This helps prevent the sticky marshmallow sauce from sticking to your fingers. And using your fingers is more effective than using a spoon to press the mixture in the pan evenly.

How to Store Rice Krispies Treats

Store the Rice Krispies treats in an airtight container on the counter. No need to refrigerate them, but you will want to keep the air from drying them out.

FAQs

Can you freeze Rice Krispies treats?

You can freeze Rice Krispies treats to keep them fresh longer. Freezing changes the taste and texture of the treat only minimally.

To freeze Rice Krispies treats, place them in a single layer on a baking sheet lined with parchment paper. Place them in the freezer for one hour. Then transfer them to a freezer-safe container or zip-top bag. Freeze them for up to 6 months.

To thaw, remove the treats from the freezer and let them sit at room temperature for about an hour.

How long do Rice Krispies treats last?

Rice Krispies treats are best eaten within two days. But eating them the day you make them is the very best. Few things are more delicious than freshly made Rice Krispies treats.

More Leftover Cake Recipes

When your freezer is full of leftover cake, try these recipes.

Leftover Birthday Cake Rice Krispies Treats

Plate of leftover birthday cake Rice Krispies treats decorated with white chocolate and jimmies.

Wondering what to do with leftover birthday cake? Make fun birthday cake Rice Krispies treats with cake crumbs, mini marshmallows, and sprinkles. Drizzle with white melting wafers to add some pizazz.

Prep Time 15 minutes
Set Time 1 hour
Total Time 1 hour 15 minutes

Ingredients

  • 6 cups of Rice Krispies cereal
  • 1½ cups of cake crumbs
  • 7 cups of mini marshmallows (pull out 1 cup for mix-ins)
  • 3 tablespoons of butter
  • ⅓ cups of Ghirardelli white melting wafers, plus more for drizzling and dipping
  • ¼ cup of jimmies

Instructions

  1. COAT a 9 X 11-inch Pyrex pan or a quarter sheet pan with shortening. Or spray it with nonstick spray.
  2. POUR the Rice Krispies cereal, cake crumbs, and 1 cup of mini marshmallows into a large mixing bowl.
  3. MELT the butter in a large pan on the stove over medium-low heat.
  4. ADD 6 cups of mini marshmallows and stir until they are almost melted.
  5. SPRINKLE in the white chocolate melting wafers and stir until the sauce is melted and smooth.
  6. REMOVE the pan from the heat and pour the sticky sauce into the bowl with the cereal, cake crumbs, and mini marshmallows.
  7. STIR to incorporate the dry ingredients into the sauce. Add the jimmies and stir to combine. (See notes.)
  8. PRESS the mixture into the greased pan. Wet your fingers under the kitchen faucet and shake off the excess water. Then use your fingers to lightly press the mixture into the pan, trying to get it as level as possible.
  9. DRY the Rice Krispies treats for about an hour. Chilling in the refrigerator can speed up the process.
  10. CUT the treats into squares.
  11. MELT the reserved white chocolate in the microwave until it is smooth. Scrape it into a zip-top baggie (or, better yet, use a decorating bag). Cut a small hole in one corner of the bag.
  12. DRIZZLE the chocolate back and forth across the Krispies treat squares.
  13. HEAT the melting wafers in the microwave at 50% power for 30 seconds. Repeat in 15-second intervals until it is smooth. Dip half of a cut treat into the chocolate and shake off the excess.
  14. SPRINKLE again with jimmies if desired. Give the white chocolate 5 minutes to dry.
  15. SERVE the treats right away.

Notes

  • Stir the jimmies in last or they might melt, which won't look as pretty. After pressing the mixture into the pan, sprinkle more jimmies on top.

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Nutrition Information

Yield

24

Serving Size

1 square

Amount Per Serving Calories 166Total Fat 5gSaturated Fat 2gTrans Fat 0gUnsaturated Fat 3gCholesterol 14mgSodium 111mgCarbohydrates 29gFiber 0gSugar 17gProtein 1g

Nutrition information is an estimate only and may vary based on individual ingredients added and cooking methods used.

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