Set Instant Pot to Sauté mode, add 2 tbsp butter or oil, then add chopped onion, and sauté for 2–3 minutes until soft.
Add garlic, ginger, and green chili. Cook for 1 more minute.
Add chopped tomatoes, spices excluding garam masala which we will add once the curry is almost done, salt, chicken thighs, and ½ cup water.
Stir well to combine then cancel sauté mode. Close the lid, set valve to sealing, and cook on high pressure for 8 minutes. Let the pressure naturally release for 5 minutes, then quick release the rest.
Remove the chicken pieces with tongs and set aside. Use an immersion blender directly in the pot to blend the sauce smooth. (Or transfer to a blender, then return to pot.)
Turn on Sauté mode (Low). Break up the chicken thighs with a spatula then stir in the cream, 2 tbsp butter, crushed fenugreek, garam masala and sugar (if using). Add more salt if needed. Let it simmer 3–5 minutes until thickened and creamy.
