Make a pastry cream filling by boiling 2 cups of milk and 1/4 cup of sugar in saucepan at medium heat and combining 1/3 cup of sugar, 1/4 cup of cornstarch and 2 egg yolks whisked with 1 egg in a bowl. Pour the milk mixture into the bowl, whisking constantly, and pour everything back into the saucepan. Once the mixture thickens, remove it from the stove, and add 2 tablespoons of butter and 1 teaspoon of vanilla extract.
To make vanilla custard filling for pastries, beat together 3 egg yolks and 3 cups of milk in a bowl, and combine 1/2 cup of sugar, 1/3 cup of cornstarch and 1/4 teaspoon of salt in a saucepan. Mix the egg yolk mixture into the cornstarch mixture, and bring the ingredients to a boil at medium-low heat for 25 minutes. Once the mixture boils, stir it for one minute, and remove the saucepan from the heat. Place the saucepan in an ice bath, and cover the custard surface with plastic wrap. Chill the custard for one hour before using.
Another type of pastry cream has a cream cheese base. To make it, combine 4 ounces of cream cheese with 3 tablespoons of sugar, and mix in 2 tablespoons of lemon juice and 8 ounces of Cool Whip whipped topping. Pipe the cream into the pastries.