Silky, vanilla-forward custard that’s rich yet balanced, perfect for filling eclairs, cream puffs, tarts, and layer cakes with a smooth, luxurious finish.
In a large heatproof bowl (preferably with a pour spout), whisk the egg yolks and cornstarch together until thick and combined; if too dry, add a few drops of the milk to bring it together. Set aside.
In a medium saucepan over medium heat, combine the milk and sugar. Whisk until the sugar dissolves and bring to a gentle simmer, then remove from heat.
Temper the eggs: Slowly stream the warm milk mixture into the yolk–cornstarch mixture while whisking constantly.
Strain the mixture back into the saucepan through a fine-mesh sieve to catch any solids.
Return the saucepan to medium heat and whisk constantly. The surface will look frothy at first; continue cooking until the cream thickens and large bubbles burst, about 1–2 minutes. Cook until pudding-like or 185–190°F (85–88°C), then remove from heat.
Whisk in the butter, vanilla extract, vanilla bean seeds, and a small pinch of salt. Let cool for 10 minutes.
Transfer the pastry cream to a heatproof bowl and press plastic wrap directly onto the surface to prevent a skin from forming.
Refrigerate until cold and set, at least 3 hours or overnight. Stir to smooth before using.