– 3 cups all-purpose flour – 1 1/2 teaspoons baking powder – 1 1/2 teaspoon baking soda – pinch of fine sea salt – 1 1/2 cups granulated sugar – 3/4 cup unsalted butter melted and cooled – 1 tablespoon vanilla extract – 3 large eggs – 2 cups sour cream – 2 cups blueberries – Zest of 1 lemon For the crumble: – 2 cups granulated sugar – 2 cups all-purpose flour – zest of 1 lemon – 3/4 cup cold unsalted butter small dice, or grated For the glaze: – 3 cups powdered sugar – 4 tablespoons lemon juice fresh squeezed – 1 teaspoon vanilla extract
Heat the oven to 350°F. Spray a 9x13 baking dish with baking spray and set aside. Mix flour, baking powder, baking soda, and salt in a medium bowl.
Mix sugar, butter, vanilla, and eggs in a large bowl until smooth. Add half of the dry ingredients to the wet components and whisk until no dry spots remain.
Stir in half the sour cream until white streaks disappear. Repeat with remaining flour and sour cream. Fold in blueberries and lemon zest; leave aside.
Whisk sugar, flour, and lemon zest in a large basin to form the streusel topping. Cut the butter in with a pastry cutter or rub it with flour with your fingers until the mixture resembles wet sand with a few pea-sized lumps.
Smooth the bottom of the pan with half the cake batter. Add half the crumb topping equally.
Spread remaining cake batter on top. Sprinkle remaining crumble over batter. Bake until a toothpick inserted into the centre comes out clean, 55–65 minutes.
Let the cake cool on a wire rack. While the cake cools, whisk powdered sugar, lemon juice, and vanilla until smooth to make the glaze.
Drizzle glaze over the cake and serve warm or room temperature.