Heat the 2 cups whole milk and 2 teaspoons vanilla extract or vanilla bean paste in a heavy bottom, medium saucepan until at a low simmer. Do not let it boil, until heat until little bubbles form around the edges.
Meanwhile, place the 2/3 cup sugar, 1/4 cup cornstarch and 1/4 teaspoon salt into the bowl of a stand mixer fitted with the whisk attachment or a large mixing bowl with a whisk, blend dry ingredients until mixed. Add the 4 large egg yolks and blend until a pale yellow.
Slowly pour the milk mixture into the eggs while whisking at a low speed. Do not mix too fast or it will froth and foam. Blend until mixed.
Transfer the mixture back to the saucepan and cook over medium-low heat for 3-5 minutes, or until thickened. Whisk continually to prevent mixture from scalding to the pan. Mix until it is thick enough to coat the back of a spoon.
As soon as the mixture thickens, remove from heat and whisk in the 1 tablespoon unsalted butter (or bourbon), if desired.
Transfer to a clean bowl and cover with plastic wrap. Press plastic wrap into the custard mixture so there is no air between the two. This prevents the filmy skin that can develop. To set faster, place in small ramekins or bowls.
Refrigerate for a minimum of 3 hours, but up to 2 days.
If you have tried this recipe, come back and let me know how it was in the comments or ratings.
Video
Notes
To use a whole vanilla bean, cut open and use 1/2 teaspoon vanilla caviar (little specs inside) in the scalded milk. You can also use a leftover, spent vanilla bean in the milk and remove before adding to egg yolks.Do not use skim or 2% milk, this really does require WHOLE MILK.Instead of butter, try adding 1 tablespoon of bourbon!Get rid of lumps by:
Stick Blender/Immersion Blender- Stick this right into the pan and blend. It might thicken the mixture a bit with agitation, just add a small amount of milk to thin it back out.
Sieve- If the mixture isn't too thick, you can push it through a mesh sieve using the back of a spoon. This will smooth out lumps or leave the big, annoying ones right in the basket.