Place the prepared blueberries in a bowl and sprinkle with lemon juice. Set aside.
Preheat the oven to 375 degrees F. Grease and flour a 9x9 inch baking dish.
In a mixing bowl, sift together the flour, baking powder, and salt. Set aside.
In a separate bowl, use an electric mixer to combine the butter and sugar. Blend in the beaten egg, vanilla and then milk. Add the dry ingredients to the liquid and stir until well blended. Gently fold in the berries.
Pour the batter into prepared pan. The batter will be thick, so just take your time in spreading it into the pan.
TOPPING
In a small bowl, combine brown sugar, flour, cinnamon and nutmeg. Sprinkle onto the batter.