01 -
Using your fingers, mix brown sugar, flour, salt, and cinnamon in a bowl, breaking up any lumps. Work in the butter until crumbly, then chill until needed.
02 -
Set the oven to 375°F and position the rack in the middle. Butter or spray a 9-inch square pan.
03 -
In a medium bowl, whisk baking powder, salt, and flour together. Keep this aside.
04 -
Take butter and sugar, and beat them for 2 minutes until fluffy. Mix in the eggs, one by one, making sure each is incorporated. Stir in the vanilla and lemon zest.
05 -
On low speed, slowly alternate between adding the dry ingredients and milk. Gently fold in the blueberries right before finishing.
06 -
Pour the batter into your prepared pan and scatter the crumble on top. Bake for 40-45 minutes, until it's golden and a tester comes out clean. Cool in the pan for 20 minutes before slicing.