Heat the water in a saucepan and dissolve the sugar in it. The amount of sugar depends on the sweetness of the mulled wine used. I took about 100 g. Remove the sugar solution from the stove and add the mulled wine and rum. Finally stir in the cold-soluble gelatine and pour the liquid into a 4 cl disposable shot cup.
Let the jello set in the refrigerator for about 3 hours.