Combine chilies, ginger, cumin seeds & mustrad seeds in a small bowl. Heat ghee in a large pot. When hot, add the spices. When the mustard seeds start to pop, drop in the potatoes & cauliflower. Fry for 4 minutes or so.
Add the tomatoes, turmeric, coriander, garam masala, sugar, salt & half the minced coriander. Mix well, cover & gently heat for 15 minutes. If the vegetables start to stick, add a few drops of water. Top with remaining coriander & serve.
Yamuna Devi, "The Art of Indian Vegetarian Cooking"