Creating the perfect diplomat cream is vital for a luscious filling in your Strawberry Tartelettes. The process begins by infusing flavor into the milk, which you bring to a boil before tempering it with a mixture of egg yolks and sugar. To thicken the mixture, cornstarch is introduced, creating a silky custard that forms the base of your diplomat cream. Once this mixture reaches the desired thickness, you stir in vanilla extract for added flavor, then allow it to cool with plastic wrap pressing directly against the surface to prevent a skin from forming. After cooling, whipped heavy cream is gently folded into the custard, yielding a light and airy texture that balances the rich components of the tart. It's crucial to ensure that the whipped cream is folded in with care to maintain its volume, resulting in an exquisite cream that complements the tartness of the fresh strawberries.