For The Streusel:
1/4 cup granulated sugar
1/3 cup light brown sugar, lightly packed
1 tsp ground cinnamon
1/8 tsp. ground nutmeg
1 1/3 cups all-purpose flour
8 tbsp (1 stick) unsalted butter, melted
For The Cake:
1 1/4 cups all-purpose flour
1 tsp baking powder
1/4 tsp baking soda
1/2 tsp kosher salt
6 tbsp unsalted butter, at room temperature
3/4 cup granulated sugar
2 extra large eggs, at room temperature
1 tsp vanilla extract
1/2 tsp grated lemon zest (or a little lemon oil)
2/3 cup sour cream
9 oz. (2 cups) fresh or frozen blueberries
Confectioners’ sugar, for dusting
To make streusel: Combine the sugars, spices and flour in a bowl. Pour in the melted butter and mix. Set aside.
To make cake: Preheat oven to 350˚F. Butter and flour a 9-inch round baking pan.
In a small bowl, sift together flour, baking powder, baking soda and salt. Set aside.
Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment on high speed until light, 4-5 minutes. Reduce speed to low and add the eggs, one at a time. Then add the vanilla, lemon zest and sour cream. With the mixer still on low, add the flour mixture until the batter is just combined. Fold in blueberries with a spatula.
Transfer batter to prepared pan and smooth with spatula. Using your fingers, crumble the streusel mixture on top. Bake for 40-50 minutes or until cake tester comes out clean. Cool completely before serving. Dust top with confectioners’ sugar.