Rinse off the potatoes, pierce the skin of each potato in a couple of places, and cook them on high in the microwave until tender.
Remove the potatoes from the microwave and let them cool for 30 minutes (or for several hours if you are not in a rush to use them).
When you are ready to make the potato curry, peel the potatoes and roughly dice them. Set aside.
In a large nonstick frying pan put the oil, mustard seeds, cumin seeds, and the fennel seeds.
Heat the oil over medium-high heat. When the mustard seeds have started popping for about 15 seconds, add the potatoes and turmeric.
Use a spatula to flip over the potatoes as they cook. Cook until you get quite a number of brown spots on the potatoes (about 8 minutes).
Sprinkle the cayenne powder and salt on the potatoes and cook and mix another minute or two.
Note: You can also make this into a wet curry by adding 1/2 cup water after you add the potatoes and turmeric. Keep adding water, 1/2 cup at a time, until you have reached the desired consistency. You may need to adjust the cayenne and salt amounts if making a wet curry. Another variation is to reduce the potatoes to 3 or 4 and add other vegetables such as carrots, peas, cauliflower and/or green beans.