1 oz of Dark rum
1/2 oz of sweet sherry (or dark sherry)
1/2 oz of grenadine syrup
3 tbsp of vanilla ice cream (or ice cream)
2 tsp of overproof rum
Blend briefly all ingredient (except overproof rum) with half a glassful of crushed ice. Pour into a collins glass, float overproof rum on top, and sprinkle with grated chocolate.