01 -
Preheat the oven to 375°F. Line a 9x9 baking dish with parchment paper and set aside.
02 -
In a medium mixing bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
03 -
In a large bowl, use an electric hand mixer to cream the granulated sugar and unsalted butter together until smooth, about 1-2 minutes. Add the egg and mix until combined.
04 -
Add the dry flour mixture and milk to the wet ingredients in alternating additions, starting and ending with the flour mixture. Mix until just combined but do not overmix.
05 -
Toss the blueberries with 1 tablespoon of flour and gently fold them into the batter. Spread the batter evenly into the prepared baking pan. The batter will be thick.
06 -
In a bowl, combine the topping ingredients by cutting the butter into the sugar, flour, and cinnamon with a fork until a crumbly texture forms. Sprinkle evenly over the batter.
07 -
Bake the cake at 375°F for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool in the pan for 10 minutes, then transfer to a wire cooling rack.