Cook the pumpkin with turmeric, chilli powder and salt. Grind the coconut, green chillies and mustard seeds.
Add the ground masala to the cooking pumpkin. When it comes to a boil, turn off the heat and add the buttermilk. Season with mustard seeds, fenugreek seeds, red chilli and curry leaves.
Add sugar to the cooking pumpkin. Let it cook until the it becomes a thick curry.