Whisk egg whites until peaks start to form.
When the peaks start forming add the vinegar, to stabilize the whites, and continue whisking until stiff. Then set aside
In separate bowl, beat the egg yolks with the sugar, water and vanilla until light.
Melt your butter in double broiler or in microwave.
Add melted butter and continue beating for another minute.
Sift in the flour and mix.
Add the lukewarm milk (if not lukewarm the butter will harden) and beat until well incorporated.
Add 1/4 of the egg white mixture and whisk with batter.
Gently fold in the rest of the egg whites using a spatula.
Grease and flour a 8x8 inch square pan or a 9 inch round pan.
Preheat oven to 325
Pour the batter into the pan and bake for 60-80 minutes or until the top is golden.
Cool in the pan for at least 3 hours.
Serve sprinkled with powdered sugar, topped with strawberries, or topping of choice.