Preheat oven to 350ºF and line a square 8-inch by 8-inch baking dish with parchment paper.
Combine flour, baking powder, and salt in a small bowl and set aside.
In a large mixing bowl, cream the sugar and butter together for 2-3 minutes until light and fluffy.
Next, beat in the eggs, sour cream, lemon juice, lemon extract, and lemon zest.
Stir in dry ingredients until just combined.
Fold in blueberries with a spatula.
Pour into your prepared pan.
Sprinkle heavily with granulated sugar on top. (Some of the sugar will soak into the coffee cake, and the rest will crust on top).
Bake the cake in the center of the oven for about 35 minutes, until browned on top and a cake tester comes out clean (I usually check the middle of the cake).
Remove from oven and let cool before serving.