Blueberry Coffee Cake

1. Preheat oven to 350°F. Grease a 9×9-inch baking dish and set it aside. 2. In a large bowl, combine the flour, sugar, baking powder, and salt. Whisk to combine and add the milk, eggs, vanilla, melted butter, and lemon zest. Whisk to break up the egg yolks and combine the wet and dry ingredients. Whisk until combined, leaving only a few dry pieces. The batter will be stiff. 3. Once combined, fold in the blueberries to evenly incorporate into the batter. Spread the batter evenly into the prepared baking dish. 4. In a small bowl, combine the light brown sugar, flour, and cinnamon. Mix with fingers and add small pieces of butter. Work the pieces of butter between thumb and fingers until the streusel resembles a coarse meal. 5. Evenly spread t he streusel over the prepared coffee cake batter. Bake in the preheated oven until the streusel is browned and the cake is domed. A skewer inserted in the middle of the cake should come out mostly clean, 40-45 minutes. Remove from the oven and cool 15 minutes before cutting and serving.