PREHEAT the oven to 425°F (220°C). Line a jumbo muffin tin with muffin papers. (See note #1.)
SIFT DRY INGREDIENTS TOGETHER: Sift the flour, salt, baking powder, baking soda, and nutmeg together. Set aside.
ZEST a clean, dry lemon.
CREAM the butter with the granulated and brown sugars with an electric mixer for about two minutes. The mixture should be light and fluffy.
MIX in the vegetable oil, vanilla extract, lemon zest, and egg until combined.
GENTLY FOLD ½ of the flour mixture into the wet ingredients with a large spatula or spoon.
POUR in ½ of the buttermilk. Stir until almost combined.
REPEAT adding the rest of the dry ingredients and then the buttermilk, gently stirring after each addition.
ADD 1 tablespoon of flour and the fresh, dry blueberries to a medium bowl. Stir until the flour coats the blueberries. Pour the blueberries through a dry mesh strainer to remove the excess flour.
CAREFULLY FOLD the flour-coated blueberries into the batter. Try not to break the blueberries. Do not over mix.
DIVIDE the batter into 6 jumbo muffin papers (about ½ cup of batter or 6 ounces). Use a muffin scoop, measuring cup, or ice cream scoop to measure. Fill the muffin paper approximately ¾ of the way full.
LIGHTLY SPRINKLE each muffin top with the decorating sugar.
BAKE at 425°F (220°C) for 5 minutes.
REDUCE THE HEAT TO 375°F (190°C) and continue baking for 18 to 25 minutes or until the muffin tops are lightly browned and a toothpick inserted in the center comes out with only a few crumbs.
PULL the muffin tin from the oven and COOL the muffins in the pan for 5 to 10 minutes.
TRANSFER the muffins from the muffin tin to a cooling rack.
COOL the muffins on cooling rack for 5 to 10 minutes.
SERVE the muffins warm with cold milk.
STORE any remaining muffins in an airtight container at room temperature for up to two days. Make sure the muffins are room temperature before placing them in a container.