Preheat the oven to 350 degrees. Grease and lightly flour an 8 x11 inch sheet tray. Heat milk and butter until the butter melts. Stir the flour and baking powder together. Put the eggs, sugar, and yolks in a bowl and set over a hot water bath, whisking until the egg mixture triples in size. Fold in the flour mixture and the milk. Pour into the prepared pan. Bake at 350 for 10 minutes.