Adapted from King Arthur Baking Companion
Yields 16 muffins
-3 1/2 cups all-purpose flour or cake flour, divided
-2 teaspoons baking powder
-1/2 teaspoon baking soda
-1 teaspoon salt
-8 tablespoons butter
-1 cup sugar
-3 large eggs
-2 teaspoons vanilla extract
-1 cup sour cream
-1 1/2 cups chopped peaches
-1 1/2 cups blueberries
Preheat the oven to 400 degrees and lightly grease 16 muffin cups or use paper liners.
In a medium-sized bowl, whisk together 3 1/4 cups flour, baking powder, baking soda, and salt, then set aside.
In a large mixing bowl, cream the butter and sugar together with a handheld or stand mixer until light and fluffy and almost white in color. Scrape down the bowl to make sure all the butter is incorporated, then add the eggs, one at a time, beating well after each addition. Add the vanilla and sour cream and mix until incorporated. Add the dry ingredients and mix on low speed just until the batter is smooth.
Toss blueberries and peaches together in remaining flour and gently fold mixture into the batter.
Fill muffin cups and bake for 18-24 minutes, until a cake tester inserted in the center comes out clean.
Remove them from the oven, cool in the pan for 5 minutes, then remove the muffins from the pan to finish cooling on a rack. (Muffins left in the pan to cool will become tough from steaming.)