Butterscotch Pastry Cream: Add 1/4 teaspoon butter-rum flavor and/or 1 cup (170g) butterscotch chips to the pastry cream after straining, stirring until the chips have melted.
Caramel Pastry Cream: Add 3/4 cup chopped caramel (213g, or 21 to 23 unwrapped individual caramels) to the hot, strained pastry cream, stirring until melted and the mixture is smooth.
Chocolate Pastry Cream: Add 1 cup (170g) chopped semisweet or bittersweet chocolate to the hot, strained pastry cream, stirring until melted and the mixture is smooth.
Hazelnut Pastry Cream: Omit the butter and increase the sugar to 3/4 cup (149g). Add 3/4 cup (234g) praline paste to the hot, strained pastry cream, stirring until combined.
Orange Pastry Cream: Increase the sugar to 3/4 cup (149g). Add 1 teaspoon orange extract, 1/4 teaspoon orange oil, or 3 tablespoons grated orange zest to the hot, strained pastry cream.
Peanut Butter Pastry Cream: Add 3/4 cup (203g) smooth peanut butter to the hot pastry cream, stirring until melted and the mixture is smooth. If you're using natural or freshly-made peanut butter, omit the butter from the recipe to prevent the pastry cream from becoming greasy.
Pistachio Pastry Cream: Omit the butter and increase the sugar to 3/4 cup (149g). Add 3/4 cup (234g) pistachio paste or blanched puréed pistachio nutmeats.