3/4 cup light brown sugar
3 cups all-purpose flour, divided
2 teaspoons ground cinnamon
1 1/2 teaspoons salt, divided
8 tablespoons (1 stick) cold unsalted butter, diced
2 teaspoons baking powder
1 stick unsalted butter, softened
3/4 cup granulated sugar
2 large eggs
1 1/2 teaspoons vanilla extract
1 lemon, zest only
1/2 cup milk
2 cups fresh blueberries
White icing (or powdered) sugar, for finishing
DirectionsPreheat oven to 375°F. Grease a 9-inch square cake pan with nonstick spray and set aside.
Combine brown sugar, 1 cup flour, cinnamon, 1 teaspoon salt and cold butter in a large bowl. Work the butter into the dry ingredients until mixture is one even color and crumbly. Refrigerate until ready to use.
Whisk 2 cups flour, 1/2 teaspoon salt and baking powder in a mixing bowl and set aside.
Beat softened butter and granulated sugar in the bowl of a stand mixer at medium speed until light and fluffy, scraping down the sides as needed. Add one egg, beat in well, then add second egg, vanilla, lemon zest and a tablespoonful of the flour mixture. Beat until thoroughly mixed. Add half the remaining flour mixture, then the milk, mixing at low speed until just combined. Add second half of flour mixture and fold in with a rubber spatula until no dry flour remains. Gently fold in blueberries. Scrape the cake batter into prepared pan. Sprinkle the chilled cinnamon streusel topping evenly across cake batter.
Bake 40–45 minutes, until a toothpick inserted into the center comes out with a few crumbs stuck to it. Cool to just above room temperature before drizzling with white icing or dusting with powdered sugar and serving.
Yields 1 (9-inch) square cake.