In a large mixing bowl, combine 3 cups plus 2 tablespoons of all-purpose flour, 1 tablespoon of baking powder, 1/4 teaspoon of ground nutmeg, 1/2 teaspoon of ground cinnamon, and 1/2 teaspoon of salt. Whisk well to ensure everything is evenly distributed.
In another bowl, use a mixer to cream together 6 tablespoons of room temperature unsalted butter, 1 cup of granulated sugar, and 1/3 cup of packed light brown sugar until it’s light and fluffy.
Add 1 large egg and 2 large egg yolks to the butter-sugar mixture, mixing well after each addition. Then, stir in 2 teaspoons of pure vanilla extract until fully incorporated.
To the wet ingredients, add the dry mixture alternately with 3/4 cup of whole milk and 1/3 cup of full-fat sour cream. Begin and end with the dry ingredients, mixing until just combined. Be careful not to overmix; a few lumps are perfectly fine!
Gently fold in 1 and 1/2 cups of fresh blueberries, taking care not to crush them. This will ensure that your muffins have juicy pockets of blueberry goodness.