Preheat oven to 175°C/350°F.
Whisk the egg replacer and sugar until fluffy before adding the coconut oil, sour cream (or soy yogurt + lemon juice) and mashed bananas.
Stir very well. Use an electric mixer but I just whisked it vigorously until completely combined.
Sift flour, cocoa powder and baking powder into the batter and stir until completely mixed.
Fill greased/lined muffin cups completely to the edge. Bake for 20-25 minutes or until a toothpick inserted in the center comes out clean.