1. Cream butter and sugar in electric mixer until very light and fluffy, about 7 minutes. Transfer to top of a double boiler over simmering water. Cook for 20 minutes, whisking often, until the mixture is silken smooth and comes away from the side of the pan when whisked.

2. Whisk 1/2 cup of the hot butter mixture into the beaten eggs, then another 1/4 cup. Whisk the egg mixture slowly into the remaining butter mixture over the heat. Cook until thickened, about 5 minutes, whisking constantly. Whisk in the schnapps and whiskey; whisk to blend. Serve warm.