Prepare the Ingredients: In a small bowl, mix the cornstarch with 2 tablespoons of milk to create a slurry. Set aside.

Heat the Milk and Cream: In a medium saucepan, combine the milk and heavy cream. Heat over medium heat until warm (about 160°F or 70°C). Do not boil.

Whisk Egg Yolks and Sugar: In a separate bowl, whisk the egg yolks and sugar until pale and slightly thickened. Add the cornstarch slurry and whisk until smooth.

Combine and Cook: Slowly pour the warm milk mixture into the egg yolk mixture, whisking constantly. Return the mixture to the saucepan and cook over medium heat, stirring constantly, until it thickens and coats the back of a spoon (about 170°F or 77°C).

Finish and Cool: Remove from heat and stir in the vanilla extract and salt. Strain the custard through a fine-mesh strainer into a bowl. Cover with plastic wrap, pressing it directly onto the surface to prevent a skin from forming. Cool to room temperature, then refrigerate for at least 2 hours before using.