- 1/2 cup unsalted butter
- 2 1/2 cups milk
- 1 cup flour
- 4 eggs separated
- 1/8 teaspoon distilled vinegar
- 1 1/2 cups powdered sugar
- 1/2 cup Nutella
Preheat the oven to 325°F. Lightly grease an 8 x8 inch baking dish.
Whip the egg whites and vinegar on high speed until stiff peaks form. Set aside.
Melt butter and set aside to cool. Warm the milk to lukewarm and set aside.
Beat the egg yolks and sugar until light in color. Beat in the melted butter and Nutella until smooth.
Mix in the flour on low speed into the batter until smooth. The batter will be very thick. By hand, whisk in the milk slowly about 1/2 cup at a time. By the time you finish, your batter will be very liquidy. If you have lumps in your batter, turn your mixer back on at low speed to beat out the lumps.
Fold in the egg whites, 1/3 at a time, trying to mix in as much egg white as possible into the batter. The batter will be lumpy, with little bits of egg whites remaining. (See my photo above).
Pour the batter into the greased pan and bake for 55-60 minutes. When you move the cake, it should shake slightly from the custard layer. If it moves too much, then the custard is not yet set. If you aren't sure if the cake is completely finished, insert a knife or toothpick and pry a little slit into a small section of the cake until you can see the custard layer to check.
Let cake cool completely (at least an hour) before cutting and serving.