1. Set aside a rimmed baking sheet for cooling pastry cream. In a medium bowl, combine egg yolks, egg, and 2 tablespoons sugar. Add cornstarch and flour; whisk until smooth and pale yellow. Set aside.

2. In a medium saucepan, combine milk and remaining 3/4 cup sugar. Stir over medium-high heat until milk begins to steam. Whisking constantly, add half the hot milk to the egg-yolk mixture. Stir until smooth; add combined mixture back to remaining hot milk in the pan. Bring mixture to a boil, whisking rapidly to prevent scorching. Remove from heat, and stir in butter and vanilla. Immediately transfer pastry cream to baking sheet, and spread into a thin layer with a large rubber spatula. Cover entire surface with plastic wrap, and transfer to the refrigerator until chilled, about 15 minutes.