1 cup whole milk
1 cup heavy cream
1/2 teaspoon vanilla extract or vanilla bean paste
6 egg yolks
1/2 cup sugar
In a large bowl, whisk egg yolks and sugar until the batter forms pretty ribbons (about 2 minutes). This will become light in color.
Fill a large bowl with ice cubes, and set aside a smaller bowl that can hold finished cream.
In a pan heat the milk, cream and vanilla. Bring to a scald over medium-high heat. (Scald = just before it boils). Stir occasionally.
Into the egg mixture, gradually add 1/2 cup of the warm milk, stirring constantly.
Now place all the ingredients into the pot with the milk and return to the stove over medium heat. At this point, it is very important to slowly and constantly stir the sauce. Keep the spoon in constant contact with the bottom of the pot.
Cook until the sauce coats the back of a wooden spoon. (Note: you can coat a wooden spoon with cream, then draw your finger across it; if cream doesn't run into the track you have created, it's done.)
Remove from heat and strain into a clean bowl and chill immediately over the ice bath.
Store in the refrigerator for up to 4 days.