Using the Temptation Chocolate Cake Mix as a base:
Substitute 1/4 cup of Kahlua and 1/4 cup hot water for the 1/2 cup of hot water called for in the package directions. I prefer it with a stronger taste of Kahlua, so I use a straight substitution of 1/2 cup of Kahlua for the 1/2 cup of hot water, but you can always start with the lower proportions to taste.
Add 1/2 cup of chocolate chips (or more, depending on your love of chocolate - err on the side of more).