Step 1

Add the milk and half and half to a pot and bring to a slight simmer. Remove from heat.

Step 2

Whisk egg yolks and sugar together in a medium bowl. Slowly ladle all the warm milk mixture into the egg yolk mixture while whisking quickly. Adding it too quickly will cook the egg yolks and cause the sauce to curdle.

Step 3

Return to the mixture to the pot and heat over medium low until the sauce thickens and coats the back of a spoon. About 5 to 6 minutes. Remove from heat, add the vanilla once it cools.

Step 4

Strain the sauce if desired. Serve warm or chill in the refrigerator.