This recipe comes from Madras, India, an area known for the manufacture of curry powder. Interestingly, you won't find any in the local cuisine—it's for export only. Instead you'll find the use of fresh curry leaves, as in this traditional South Indian recipe.
2–3 tbsp. vegetable oil
1 tsp. brown mustard seeds
2 tbsp. urad dal
1–3 dried hot red chiles, halved lengthwise
20 fresh curry leaves (optional)
2 medium onions, quartered and thinly sliced
1 tsp. salt
1⁄2 tsp. ground turmeric
1⁄2 tsp. cayenne
1 lb. potatoes, peeled and cut into 1⁄2" dice
1 tomato, chopped
Pinch of ground asafetida
1. Heat vegetable oil in a well-seasoned wok or a large nonstick frying pan over medium heat. Add mustard seeds, urad dal, and chiles. Stir until the seeds start to pop and the dal begins to turn red, a few seconds.
2. Stir in curry leaves, if using. Add onions, and fry until the edges begin to brown. Add. salt, turmeric, and cayenne, and stir for 5 seconds. Add potatoes, then stir and fry for 2 minutes.
3. Add tomato and asafetida. Stir-fry for 1 minute. Add 1 cup plus 2 tbsp. water and bring to a boil. Cover, reduce heat slightly, and cook vigorously until the potatoes are just tender and the water is absorbed. Remove lid, stir, and fry, turning potatoes over often, until they are reddish yellow, 5–8 minutes.