2 1/2 cups all-purpose flour
2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
12 tablespoons (1 1/2 sticks) unsalted butter, at room temperature
1 1/2 cups sugar
3 large eggs
1 1/2 teaspoons pure vanilla extract
8 ounces sour cream
1/4 cup milk
3 cups (1 1/2 pints) fresh or frozen blueberries, stems removed
For the topping(see below), in a medium bowl, stir together the flour, cinnamon, and brown sugar. Add the butter pieces and combine the mixture with a fork until the topping resembles coarse crumbs. Set aside.
Preheat oven to 350°F. Place paper liners in muffin pans. In a separate medium bowl, sift together flour, baking powder, baking soda, and salt.
With an electric mixer fitted with a paddle attachment, cream the butter and sugar until light and fluffy, about 5 minutes. At low speed, beat one egg in at a time, then add vanilla, sour cream, and milk until combined. Add 1/3 of dry ingredients at a time and beat until just combined. With a spatula, evenly fold blueberries into batter.
Scoop batter into muffin pans and fill each cup to the top. Sprinkle topping evenly over batter. Bake for 30 to 35 minutes, until a cake tester or wooden skewer comes out clean.
Makes 24 muffins
1/2 cup all-purpose flour
1 teaspoon ground cinnamon
1/2 cup firmly packed light brown sugar
4 tablespoons (1/2 stick) unsalted butter, slightly softened and cut into 1/2-inch pieces