Put potatoes in a large pan and cover with cold water. Bring to a boil, and cook for 10 minutes or until potatoes are tender but not disintegrating.

Add salt,onion, garam masala and chili powder to a bowl. Squeeze about 2 tablespoons of lemon juice into the onion mixture. Reserve a few springs of coriander for garinsh. Chop the remaining coriander and add to the bowl.

Drain the potatoes and add them to the bowl. Mash everything together, and form into 8 patties. Heat butter and oil in a pan until it sizzles. Add the patties and fry for 2 to 3 minutes on each side or until golden and crisp. Drain patties on paper towels and serve hot.