Puree the cherries, except for 4 pieces, with the juice in the pot and bring to the boil while stirring. Stir the starch and 1 tbsp. water until smooth, use to bind the cherry puree slightly. Let cool off.
Peel 1 bar (approx. 20 g) of chocolate with a peeler as a roll, put aside. Heat the milk. Break the remaining chocolate into pieces and melt in a hot water bath. Carefully add the milk while stirring.
Let it cool down.
Whip the cream until stiff and fold into the liquid chocolate. Lay the chocolate mousse and cherry puree alternately in four glasses. Stir the puree and mousse in the glasses with a spoon handle to create a swirl.
Chill for about 2 hours.
Decorate the mousse with 1 cherry and 1 chocolate roll each.