I didn't have any sherry open, but this is also excellent with Carpano Antica. I used a cocoa-nib infused Campari and the Real McCoy 5 year rum. I'm eager to try it with the amontillado next time I have a bottle.
I followed Anita's advice and added an ounce of cream (because I misread her comment), which makes for a lot of drink, but I'm not complaining. It's still plenty boozy and not too sweet. I added some chocolate bitters to the top.
Used Antica and my new Sirene Chocolate liqueur from Sheringham distillery in Victoria, B.C., and Scrappy's chocolate bitters. Dang, this is an excellent drink. It's like a decadent after-dinner drink but not overly sweet and still a Manhattan at heart.