3/4 cup milk
6 large egg yolks
1 cup granulated sugar
4 teaspoons instant coffee powder
1 tablespoon vanilla extract
2 cups unsalted butter, softened (no substitutes)

Heat milk in medium saucepan over medium heat just to boiling.

Whisk egg yolks and sugar together in medium bowl. Gradually whisk in hot milk. Return mixture to sauce pan and cook, stirring constantly over medium/low heat, until it thickens and coats the back of a spoon (about 6 minutes). DO NOT BOIL! Strain through a sieve into a mixer bowl. Stir in coffee powder and vanilla and let set to room temperature. Beat in 2 cups butter, 1 tablespoon at a time, beating well after each addiction. Frost a cake.