Stir powdered gelatin into 2 tablespoons of cold water in a small dish and leave it to soften for 10 minutes. 2 teaspoons gelatin powder
In a medium saucepan, heat the milk on medium heat until it is just at a simmer. Don't let it boil. 480 g whole milk
While the milk is warming, add the egg yolks, vanilla, sugar, salt, and cornstarch to a separate bowl. Whisk until glossy and smooth. 4 large egg yolks, 65 g granulated sugar, 1 vanilla bean, 30 g cornstarch, 1/4 teaspoon salt
Place the bowl on a dampened kitchen towel. Once the milk is hot, pour the hot milk in a steady stream into the egg mixture while whisking constantly.
Return the combined mixture to the saucepan over medium heat. Cook the custard, whisking constantly, until it starts to bubble. Once bubbling, keep it at a boil and whisk for a full minute. This is essential to deactivate the amylase enzyme in the egg yolks, which would otherwise cause the custard to become soupy as it cools.
Take it off the heat and whisk in the butter and gelatin until smooth. 45 g unsalted butter
Pour the pastry cream into a clean bowl (push it through a fine-mesh sieve first for extra smoothness). Lay plastic wrap directly onto the surface of the custard and let it cool to room temperature.