01 -
Grab a small bowl and mix the brown sugar, flour, cinnamon, and salt. Use your hands to break up any clumps in the brown sugar. Work the cold butter chunks into the mix until it feels crumbly. Pop it in the fridge for later.
02 -
Set the oven to 375°F and place the rack right in the middle. Butter a 9-inch square baking pan or use a spray that won’t stick.
03 -
In a medium-sized bowl, whisk the flour, baking powder, and salt together. Set it aside for now.
04 -
Beat the butter with granulated sugar until it’s nice and creamy, about 2 minutes. Add eggs one at a time, mixing well after each. Finally, stir in the vanilla and the lemon zest.
05 -
Take turns adding the flour mixture and milk to the wet ingredients, starting and finishing with the flour mixture. Keep the mixer on a low setting while you do this. Gently fold in the blueberries so they’re evenly spread out.
06 -
Pour the batter into the prepared pan and sprinkle the streusel topping over it. Bake for 40-45 minutes, until the top is golden and a tester comes out clean. Let it cool in the pan for 20 minutes before serving.