Prepare your espresso or coffee.
Take off the heat and use a milk frother to froth the milk until it is about double in size.
The recipe works best as is. I tried halving it and the flavor balance wasn't quit the same.
I've tried this with both Kahlua and Godiva Chocolate Liqueur. Technically Kahlua is Rum + Coffee Liqueur, but surprisingly it's the one that had more chocolate overtones. Both tasted delicious though.