Preheat oven to 350 degrees F (175 degrees C). Butter and flour a springform pan.
Sift 2 cups flour, baking powder, and salt into a bowl.
Beat 1/4 cup butter, 3/4 cup sugar, and egg with an electric mixer in a large bowl until smooth. Gradually add milk and beat until fluffy; stir in flour mixture, making a stiff batter. Gently fold in blueberries and spread batter into prepared springform pan.
Mix 1/2 cup sugar, 1/3 cup flour, cinnamon, and 1/4 cup butter in a bowl until blended and crumbly in texture.
Sprinkle on top of batter, then lightly press topping into batter using fingertips.
Bake in preheated oven until golden and a toothpick inserted in the middle comes out with moist crumbs, about 40 minutes.
