Chop the chocolate coating and melt over a warm water bath. Dip 4 spoons into the couverture, place on baking paper and chill. Put the rest of the couverture into a small disposable piping bag.
Spray 4 glasses inside with it, refrigerate. Whisk egg yolk and sugar with the whisk of the hand mixer until thick and creamy, stir in rum. Add 400 ml boiling water and stir in. Pour into the glasses.
Place one scoop of ice cream in each glass and serve immediately with the chocolate spoons.