Start by filling a shot glass 2/3 full of chilled Licor 43. (I recommend using a shot glass that looks like a mini beer glass for the full effect. I’ve linked a few of my favorites in the note section below.)
Then, create the “foam head” by adding a layer of heavy cream to the top of the Licor 43. You can do this by pouring on the cream very slowly. Another option is to pour the cream over the back of a spoon.