Pastry Cream, also known as crème patisserie, is a staple in pastry kitchens. It is used as a filling for tarts, pastries such as éclairs and Napoleons, cakes and other desserts such as a traditional Boston Cream Pie. Pastry Cream is rich cooked custard made with eggs, milk, sugar, flour or cornstarch for a thickener, and normally a vanilla bean for flavoring, then chilled before using. Pastry cream may also be flavored with other flavors such as chocolate, coffee, fruit purees, or liqueurs. Pastry Cream is best used within 3 days of preparation.