https://www.youtube.com/watch?v=rRPp8yngXpo

1/3 C + 1 T sugar
2 T cornstarch
1/8 t salt
3 egg yolks
2 1/4 C whole milk
3 T unsalted butter
2 t vanilla

1. In a small pot, add the sugar, cornstarch and salt and whisk together to
   mix.
2. Add 1/4 C of milk and whisk to dissolve everything.
3. Add the rest of the milk and egg yolks and whisk to mix.
4. Heat on medium for about 6 minutes, whisking occasionally.
5. Turn heat down to medium low and stir constantly until it's been boiling
   for 2 minutes.
6. Take off heat and mix in the butter and vanilla.