Combine the vodka, coffee liqueur and Irish cream in a shaker.
Add ice and shake hard for 10 seconds.
Strain over fresh ice in an old-fashioned glass.
Grate a little nutmeg over the surface.
Credited to the Wreck Bar at Rum Point on Grand Cayman in the 1970s. Shaken it is a cocktail; blended with ice cream it is the frozen version that colonised resort bars. Both are legitimate — the shaken one is the drink.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Mudslide.