1.
Put all ingredients except the baking soda and the chocolate into the bowl of the stand mixer and beat everything into a homogeneous batter.
2.
Let the batter rest for at least 4–6 hours so the sourdough starter can take effect.
3.
Preheat the oven to 180 °C fan.
4.
Add the baking soda and the finely chopped chocolate to the batter.
5.
Stir the batter and spoon it into cupcake liners.
6.
Put the cupcakes in the oven for 15 minutes and test with the tip of a knife to see if they are baked through.
7.
Let the cupcakes cool on a wire rack.
8.
Prepare the topping by mixing the cream cheese with the cocoa and the sugar. Put the mixture into a piping bag with a nozzle and decorate the top of each cupcake with some cream.