Parboil potatoes in salted water, strain and set aside. Save ½ cup of potato water before straining.
Heat ghee or butter in a large skillet on medium heat, fry cumin and fennel seeds for a few minutes before adding onions, garlic, and a pinch of salt. Continue cooking onions while stirring regularly until they are translucent.
Add tomatoes, curry powder, and chile powder. Stir until combined, add bay leaf, cover pan, and simmer for 5-10 minutes.
Mash everything with a flat spoon or spatula until it is formed into somewhat of a paste. Add potatoes and leftover potato water, stir until curry paste and water have formed a nice consistency. Cover and simmer for another 5-10 minutes until potatoes are tender and can be pierced with a fork.
This is a versatile recipe and the spices can be modified. Try adding whole mustard seeds or charnushka seeds to the first step. To thicken the liquid/sauce, try mashing a potato chunk into a paste agains the side of the pan. For an even richer sauce, try adding heavy cream or yogurt to the dish when you simmer the potatoes.