Heat the cream and whiskey in a medium-size saucepan until it is nearly boiling. In a medium-size bowl, whisk together eggs, sugar, cornstarch and salt. Add a small amount of the warm cream into the egg mixture and whisk quickly to incorporate all of the ingredients. This will temper, or warm, the eggs so that they don’t cook too quickly and scramble.
Once tempered, pour the egg mixture into the rest of the cream, whisking constantly as you pour them together. Continue whisking for about 2 minutes. The mixture will thicken slightly. Remove from the heat and stir in butter and vanilla.
Allow the mixture to cool to room temperature. If you have a few lumps in your custard, strain custard through a fine-mesh sieve.
Cover with plastic wrap and refrigerate for 2–3 hours. To avoid having a custard “skin” cover over the top, be sure to press the plastic wrap right onto the warm custard before refrigerating.
Recipe courtesy of Hello, Donuts!