In a small bowl, stir together the flour, sugars, and cinnamon. Using a fork or your fingers, work the butter into the flour mixture until crumbly. Chill until ready to use.

Preheat the oven to 375°F. Grease an 8×8-inch baking pan with baking spray.

In a medium bowl, whisk together flour, baking powder, and salt.

In a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, combine the butter, sugar, and lemon zest. Beat on medium speed until light and fluffy, 2 to 3 minutes. Add the eggs, one at a time, stopping to scrape down the sides of the bowl occasionally. Beat in the vanilla.

With the mixer on low speed, add a third of the flour mixture to the butter mixture. Pour in half of the milk, beating until just incorporated. Repeat, alternating with the milk and flour mixture. Fold in 2 cups of blueberries.

Spread the batter into the prepared baking pan. Sprinkle with the chilled streusel topping and the remaining ½ cup of blueberries.

Bake for 50 to 55 minutes, tenting after 25 minutes, or until the top is golden brown, and a wooden pick inserted into the center comes out clean. Let cool for at least 20 minutes before slicing and serving.