Whisk together first 4 ingredients in a 3-quart saucepan. Gradually whisk in half-and-half. Cook over medium heat, whisking constantly, until mixture comes to a boil. Cook 1 minute or until mixture is thickened and bubbly. Remove from heat; whisk in butter and vanilla. Cover and chill 4 hours.
Peanut Butter Pastry Cream: Omit 2 tablespoons butter, and stir in 1/3 cup creamy peanut Butter.
Coffee Pastry Cream: Stir 1 tablespoon instant coffee granules in with half-and-half.
Grand Marnier Pastry Cream: Omit vanilla extract, and stir in 2 tablespoons orange liqueur.