Black Cadillac

We had one spare egg left over from the the weekend's recipes, so I wen looking for a cocktail with egg in it and found the
Black Cadillac. Naturally, I had to substitute a different dark beer, as well as a different scotch, a different rum and a different syrup. Oh and different bitters. But the egg was as specified!
I discovered that shaking a cocktail with a lot of beer in it leads to some rather explosive results, and that it is important to pour out the result properly if you want to keep the frothy head.
This had a fairly strong coffee taste, which I can only assume came from a combination of the beer and the Mole bitters I used. But it was not too alcoholic and nice, quaffable alternative to the powerful after dinner drinks we've been having.