Preheat the oven to 180°C.
Prepare a loaf pan (25cm x 10cm), line it with baking paper.
In a medium bowl mix dry ingredients (except for the sugar): wholemeal spelt flour, potato starch, cacao powder, baking powder, soda and salt.
Grate the courgette and set aside.
Using a stand mixer (or hand mixer), beat the whole eggs until fluffy (about 6-8 min). Continue mixing and add the sugar, spoon at the time (about 2 min). Continue mixing and very slowly pour the oil into your batter.
Reduce the speed to low, add the dry ingredients and mix just until combined.
Add the grated courgette and chopped milk chocolate (optional) to the batter and mix everything with the spatula until combined.
Pour the batter into the loaf pan lined with baking paper and bake for 60-65 minutes or until dry toothpick.