Slowly melt the chocolate together with the sugar and butter in a bowl in a double boiler. Meanwhile, grease the glasses with butter and preheat the oven to 160 degrees.
When the chocolate mixture is completely liquid, gradually stir in the eggs. Then add the rum aroma or the rum. Mix the flour with the baking powder and add to it. Mix everything briefly. Then pour the mixture into the greased glasses with a tablespoon and bake in the hot oven for 20-25 minutes.
Since the cakes rise, the glasses should only be filled to about 3/4 full. The batter is enough for 8 jars of 220 ml each. To store the jars, they must be closed immediately (i.e. still hot) with a rubber ring and the appropriate lid. The cakes then keep for about 2 - 3 weeks.