Preheat oven to 325 degrees. Grease and line an 8 inch by 8 inch baking dish with parchment paper.
Separate eggs and add the egg whites to a mixer and beat egg whites until stiff. Place egg whites in a bowl and set aside. Beat egg yolks and sugar until light. Add butter and vanilla. Beat for 2 minutes,
Add flour and mix it in until fully incorporated. Slowly start adding the milk and beat until everything is well mixed together. With a spatula, fold egg whites, 1/3 at a time.
Pour batter into baking dish and bake for approx 60 minutes or until the top is lightly golden. Cool and dust heavily with powdered sugar.