for the Cake
2 cups all-purpose flour plus 1 teaspoon
1 tablespoon baking powder
1 teaspoon table salt
16 tablespoons unsalted butter (2 sticks), softened to room temperature
3/4 cup packed light brown sugar
1/2 cup granulated sugar
3 large eggs
1 cup whole milk
1 cup blueberries, fresh or frozen
for the Topping
1/2 cup blueberries, fresh or frozen
1/4 cup granulated sugar
1/2 teaspoon ground cinnamon
Adjust oven rack to middle position and heat oven to 350F. Create a foil sling for your 9 x 13 baking pan; grease and flour, and set aside.
Whisk 2 cups flour, baking powder, and salt together in medium bowl. With electric mixer, beat butter and sugars on medium-high speed until fluffy, about 2 minutes. Add eggs, one at a time, beating until just incorporated. Reduce speed to medium and beat in one-third of flour mixture until incorporated; beat in half of milk. Beat in half of remaining flour mixture, then remaining milk, and finally remaining flour mixture. Toss blueberries with remaining 1 teaspoon flour. Using rubber spatula, gently fold in blueberries. Spread batter into prepared pan.
For the topping: Scatter blueberries over top of batter. Stir sugar and cinnamon together in small bowl and sprinkle over batter. Bake until toothpick inserted in center of cake comes out clean, 45 to 50 minutes. Cool in pan 20 minutes, then turn out and place on serving platter (topping side up). Serve warm or at room temperature.