"A yummy curry learned from the women in my village when I was living in Sri Lanka. It is a basic recipe meaning that you can add more or less of items to suit your taste. Every batch of parripu is personalized to whoever cooks it. Careful! It tends to be very spicy so if you are sensitive reduce the chile amounts."
Heat oil and butter in a saucepan over high heat until butter is melted. Add onions, Thai chiles, garlic, curry leaves, and cinnamon stick. Saute until onions are soft and translucent, 5 to 7 minutes.
Remove cinnamon stick from the onion mixture. Add water and bring to a boil. Stir in lentils, curry powder, and ground red chile, Reduce heat to low; cover and let curry simmer until water is mostly evaporated, 10 to 15 minutes.
Pour coconut milk into the curry. Season with salt. Continue simmering until curry is thick but not dry, about 10 minutes.