Discard the ends or keep them. Make a slit in the center of the chilies and remove the seeds and the pith.
Heat vegetable oil in a large shallow frying pan over medium-high heat.
Fry the chilies from all sides until blisters appear on their surface.
Dry roast peanuts, sesame seeds, cumin seeds, coconut, and dry red chilies over medium heat until lightly browned and fragrant (3-4 minutes), stirring frequently.
Add the cooled ingredients to a blender along with ginger, garlic, and ½ cup water, and blend to make a fine paste.
Scrape the sides of the blender a few times while blending.
Heat oil in a pan over medium-high heat. Once the oil is hot, add mustard seeds, fenugreek seeds, and curry leaves, and let them crackle for 3-4 seconds.
Add onions and fry until they turn golden brown (6-8 minutes), stirring frequently.
Add the salan paste, coriander powder, turmeric powder, red chili powder, and salt, and saute for 1-2 minutes.
Add 2 cups of water and bring the curry to a boil.
Reduce the heat to low and cover the pan with a lid. Cook the curry for 15-20 minutes.
Now remove the lid and add the fried chilies to the pan and stir well. Cover and cook for another 8-10 minutes.
Stir in tamarind paste and jaggery and cook for a minute.
Check for salt and add more if needed. Mirchi ka salan is ready. Garnish with cilantro and serve it with biryani, rice, or roti.