1/4 cup granulated sugar
1/3 cup light brown sugar, lightly packed
1 teaspoon ground cinnamon
1/8 teaspoon ground nutmeg
1/4 pound (1 stick) unsalted butter, melted
1 1/3 cups all-purpose flour
6 tablespoons unsalted butter, at room temperature (3/4 stick)
3/4 cup granulated sugar
2 extra-large eggs, at room temperature
1 teaspoon pure vanilla extract
1/2 teaspoon grated lemon zest
2/3 cup sour cream
1 1/4 cups all-purpose flour
1 teaspoon baking powder
1/4 teaspoon baking soda
1/2 teaspoon kosher salt
1 cup fresh blueberries
Confectioners' sugar for sprinkling
Preheat the oven to 350 degrees F. Grease a 9-inch round baking pan with butter then dust with flour; set aside.
Make the streusel first. Combine the granulated sugar, brown sugar, cinnamon, and nutmeg in a bowl. Stir in the melted butter and then the flour. Mix well and set aside.
For the cake, cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment on high speed for 4 to 5 minutes, until light. Reduce the speed to low and add the eggs 1 at a time, then add the vanilla, lemon zest, and sour cream.
In a separate bowl, sift together the flour, baking powder, baking soda, and salt. With the mixer on low speed, add the flour mixture to the batter until just combined. Fold in the blueberries and stir with a spatula to be sure the batter is completely mixed.
Spoon the batter into the prepared pan and spread it evenly with a spatula.
With your fingers, crumble the prepared streusel evenly over the batter. Bake for 40 to 50 minutes, until a cake tester comes out clean. Cool completely. Sprinkle confectioners' sugar on top before serving.
Place leftover Blueberry Crumb Cake in an air tight container and store in the refrigerator.