Heat Milk Mixture: In a clean pot, combine milk, vanilla extract, dulce de leche, sugar, and salt. Heat until just below boiling, stirring occasionally.
1 1/3 cups milk, 3 tablespoons sugar, 1/2 cup dulce de leche, 1 teaspoon vanilla extract, 1/4 teaspoon salt
Prep Yolks: While the milk heats, whisk yolks, cornstarch, and 2 tablespoons of the milk mixture (while it's still lukewarm) in a bowl until smooth.
4 egg yolks, 3 1/3 tablespoons cornstarch
Temper Eggs: Gradually whisk hot milk into yolk mixture in small additions to avoid curdling.
Thicken Cream: Return the mixture to the pot and cook over medium heat, stirring constantly, until thickened and bubbling (2–4 minutes).
Whisk Off Heat: Remove from heat and whisk for about a minute until smooth.
Add Butter: Stir in butter until fully melted and incorporated.
2 tablespoons unsalted butter
Taste and Adjust: Taste while hot and add sugar or salt if needed.
Strain if Desired: Strain through a mesh sieve for extra smoothness.
Cool: Cover with plastic wrap touching the surface to prevent a skin. Cool at room temp for 30–60 minutes, then refrigerate.
Whisk and Use: Break up the chilled cream with a fork and whisk until smooth before using.
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Notes
This pastry cream keeps well in the fridge for up to 3 days.