Peel the watermelon, cut into small pieces, core and puree the pulp in a blender. Measure out 800 ml.
Mix the cornstarch with a little melon juice and place in a saucepan with the remaining juice and the other ingredients except the chocolate droplets. Bring to the boil and simmer for 2 - 3 minutes, stirring constantly.
Put the mixture in a large pudding form or in small molds and let set in the refrigerator for a few hours, turn out onto dessert plates and serve decorated with the chocolate droplets.