Grate the extra dark chocolate, or mince using the food processor.
To a large bowl, add the dry ingredients: the flour, the cornstarch, the sugar, the cocoa, the extra dark chocolate and mix well. Set aside. To a separate bowl add the liquid ingredients: the soy milk and the sunflower oil. Mix well. Add the liquid ingredients to the dry ingredients and stir until just combined in a soft batter.
Take a glass, add the apple cider vinegar and the cream of tartar, mix and quickly pour over the batter. Stir well.
Insert the paper or silicone muffin cups into the pan. Spoon the batter into the muffin pan, filling each cup about two-thirds full.
Sprinkle the tops of the muffins with some coconut flour.
Bake in a preheated oven on 180°C. for 30-35 minutes. Set aside to cool down.
Notes
I normally use the soy milk with no sugar for this recipe but any kind of plant-based milk can be used.Sometimes I add at the obtained batter some walnuts or hazelnuts, that I collected in the woods behind my house.Coconut flour gives a few of color and an interesting aftertaste, but not everyone likes it. The recipe also works well without coconut flour.