Preparation Steps

• Preheat your oven to 375°F (190°C). Grease and flour an 8x8 inch (20x20 cm) baking pan or a 9-inch (23 cm) round pan.
• To make the streusel: In a small bowl, combine 0.5 cup all-purpose flour, 0.25 cup granulated sugar, 0.25 cup packed light brown sugar, and 0.5 teaspoon ground cinnamon. Cut in 0.25 cup cold butter with a pastry blender or your fingertips until the mixture is crumbly. Set aside.
• To make the cake batter: In a large bowl, whisk together 1.5 cups all-purpose flour, 0.75 cup granulated sugar, 2 teaspoons baking powder, and 0.5 teaspoon salt.
• In a separate medium bowl, whisk together 0.5 cup whole milk, 0.5 cup melted butter, 1 large egg, 1 tablespoon lemon zest, and 1 teaspoon vanilla extract.
• Pour the wet ingredients into the dry ingredients and mix until just combined. Be careful not to overmix the batter. Gently fold in 1 cup of blueberries.
• Pour the batter into the prepared baking pan and spread it evenly. Sprinkle the streusel topping generously over the batter.
• Bake for 35-45 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out clean.
• Let the coffee cake cool in the pan on a wire rack for at least 15 minutes before serving.
• To make the optional lemon glaze: In a small bowl, whisk together 1 cup powdered sugar and 2 tablespoons fresh lemon juice. Add milk 1 tablespoon at a time until your desired drizzling consistency is reached. Drizzle the glaze over the cooled coffee cake before serving.