Boil the potatoes in their jacket and allow to cool thoroughly. The potatoes can be boiled and left in the refrigerator for 2-3 days. Peel the potatoes and cut them into 2-inch squares.
Blanch the cauliflower in boiling water for 2 minutes; do not over- boil the cauliflower as it should remain firm after cooking. Allow the cauliflower to cool and cut it into 1/2-inch diameter florets.
Heat the oil over medium heat in a wide shallow pan, preferably non-stick or cast iron. Add the mustard seeds, and as soon as they begin to pop, add the cumin and fenugreek seeds and then the red chilies.
Add the onions and the green chili; stir and fry until the onions are golden brown (8-10 minutes). Add the cauliflower; reduce heat to low. Cover the pan and cook for 6-8 minutes.
Add the potatoes, turmeric, cumin, coriander and salt. Stir gently until all the ingredients are mixed thoroughly. Cover the pan and cook until the potatoes are heated through (6-8 minutes). Stir in the coriander leaves (if used) and remove from the heat.
