Mix together chickpeas flour, chili powder and ground coriander. Add salt, black pepper and the beaten egg. Let rest.
Meanwhile prepare the yogurth sauce. Peel the ginger and mince with the clove garlic. Fry with butter for a couple of minutes. Mix gently with the yogurth in a bowl. Garnish with mustard seeds.
Mince the onion, bell pepper and peeled potato. Add minced vegetables and baking powder to the besan mixture.
Heat oil in a frying pan. Take a spoonful of mixture and put it in the pan. Fry over medium heat, turning carefully when golden brown.
Serve hot with the yogurth sauce.