In a bowl, whisk together the egg yolks and sugar until pale and light in color.

Add the cornstarch and whisk until smooth and fully combined.

In a saucepan, gently warm the milk and heavy cream over medium heat. Add the vanilla extract.

Slowly pour the warm milk mixture into the egg yolk mixture while whisking constantly.

Return the mixture to the saucepan and cook over medium heat, whisking continuously, until the pastry cream thickens.

Remove from the heat and let it cool slightly.

Pass the pastry cream through a fine-mesh sieve into a clean bowl to remove any lumps.

Press plastic wrap directly onto the surface and let the pastry cream cool completely before using.