Rinse the horse gram and soak in it 2 cups of water for atleast 8 to 10 hours.
After 8 hours, drain the water and add 1.5 cups of freshwater and pressure cook for 3 to 4 whistles in a stove-top pressure cooker. If using Instant Pot, directly cook in the pot for 18 to 20 minutes and release the pressure naturally.
Drain the water, and do not discard it thought. You can use it for kollu rasam.
Set aside the cooked sundal.
Pulse the roasted peanuts coarsely. Make sure there are a few whole peanut pieces just for texture and crunch.
Heat a pan and add the coconut oil. When it is hot, add the mustard seeds, urad dal, chana dal, hing, curry leaves, and dried red chilies.
Let the mustard seeds splutter and then add the cooked horse gram and salt. Mix well and cook until the moisture is all absorbed, for about 2 to 3 minutes.
Now add the peanut powder and coconut. Mix well and make sure the horse gram, peanut powder, and coconut are well combined. Cook for a couple of minutes and turn off the heat. That's it. Kollu sundal is ready.
Serve right away. It works well as a side dish for rice also.
Notes
As I used salted peanuts, I used less salt. Please adjust accordingly. The same goes for dried red chilies as well.
Instead of dried red chilies, you can use ½ heaped tsp of sambar powder or rasam powder or red chili powder to spice up the sundal.
Coconut oil always adds flavor, but you can use oil of your choice.