Whisk the egg yolks with sugar and vanilla for about 2 minutes, until you get a light, fluffy mixture.
Slowly incorporate sifted cornflour into the egg mixture, and whisk until it’s fluffy, smooth and well combined, about 2 minutes.
Heat the milk over low heat until you see the first bubbles, then remove it immediately from the heat.
Drop the egg mixture gently over the hot milk and return the pan over low heat. Do not stir.
Wait a few seconds, the egg mixture will float over the milk surface (because the whipped mixture has incorporated enough air to remain on the surface).
In about 30 seconds milk bubbles will pierce the surface of the egg mixture and it will slowly incorporate it.
When most of the surface is covered with milk, turn the heat off, take the pan away from the heat, and immediately whisk the mixture vigorously for about 30 seconds.
While you whisk, the mixture will almost immediately turn into pastry cream. It should be thick, creamy and smooth.
Transfer your crema pasticcera into a ceramic or glass casserole dish or a baking pan, and cover with plastic wrap, making sure it touches the surface of the cream.
Once cooled down, the crema pasticcera has a thick smooth texture and holds its shape, and it’s ready to be served or used in other dessert recipes.