Spray a 9 inch cake pan with non-stick cooking spray, and preheat the oven to 350 degrees.
Combine the brown sugar and 2 tablespoons of butter in a hot saucepan until they combine.
Distribute the sugar and butter mixture in your cake pan, to make a thin layer at the bottom.
Add the blueberries in a layer on top of the sugar and butter mixture.
Separate the egg whites and egg yolks. With an electric mixer, beat the egg whites until stiff peaks form. Set aside.
With an electric mixer, cream the sugar and butter until well combined. Add the egg yolks and vanilla, making sure everything is well mixed.
In a separate bowl, mix the flour with the salt and baking powder. Add the flour mixture and the milk to the batter. Fold in the egg whites.
Bake for 55-60 minutes.
After cooling for 20 minutes, flip the cake over onto a serving plate. Serve warm.