1. Cream together the butter and sugar until well combined. Then add the egg yolks, whiskey, and vanilla, mixing until thoroughly blended.
2. Gradually incorporate sifted all-purpose flour along with baking powder and salt, alternating with the milk.
3. Beat the egg whites until stiff peaks form, and gently fold them into the batter.
4. Grease and flour a cake pan, pour in the batter, and bake in a preheated oven at 180 degrees Celsius (350 degrees Fahrenheit) for 1 hour.
5. Unmold the cake while still warm.
Enjoy the delightful aroma and rich flavor of this homemade butter cake!
