Heat oil in a deep-fryer or large saucepan to 375 degrees F (190 degrees C).
Whisk gram flour, salt, cayenne pepper, cumin seeds, and baking powder together in a bowl. Stir lukewarm water into flour mixture, 1/2 cup at a time, until batter has a thick pancake-batter consistency.
Dip potato slices in batter until well-coated.
Working in batches, cook coated potatoes in hot oil, turning once, until golden and crispy, 2 to 4 minutes. Transfer potatoes to a paper-towel lined plate to drain.
The nutrition data for this recipe includes the full amount of the batter ingredients. The actual amount of the batter consumed will vary. We have determined the nutritional value of oil for frying based on a retention value of 10% after cooking. The exact amount will vary depending on cooking time and temperature, ingredient density, and the specific type of oil used.