Step by step
In the meanwhile, make your custard: work egg yolks and sugar until foamy. Pour over milk and sifted flour. Put on a low heat, stirring constantly until the mixture begins to steam and thicken. Use a piping bag to stuff your pastries with the custard.
Tips
You can stuff your profiteroles with Italian custard, cream, Chantilly cream, chocolate cream. You can also freeze your cream puffs, provided that you'll defrost them in advance before serving them.
Trivia
Profiterole is a French word that means "small cream puff". In the classic recipe, profiteroles can be stuffed with a either sweet or savoury cream. That's why profiteroles can be an appetizer and a dessert as well. The famous "mountain" of profiteroles is a cake called Saint Honorè