For the plum cupcake, rinse the plums with cold water and rub dry. Cut into wedges, removing the pit. Place in a saucepan with lemon juice and zest, port wine, cloves, cinnamon and preserving sugar and simmer for about 10 minutes. Remove the clove and puree the plum puree with a hand blender. Set aside 4 tablespoons of plum puree.
Mix flour, sugar and cooking soda. Stir in milk and plum puree. Line a baking tray with baking paper and spread the mixture on it. Bake in the preheated oven at 200 °C for about 20 minutes. Let cool and spread with the remaining plum puree.
Melt the chocolate with butter or coconut oil in a water bath and coat the plum cake with it.