Indian Crockpot or Instant Pot Coconut Chicken Curry

Piggy-backing on my latest Indian food in a Crockpot success story, Beef Vindaloo, I decided to try a chicken curry cooked with coconut milk. This was my husband's response upon tasting it: "it really is amazing that you can make up recipes that taste like restaurant-quality Indian food." This is probably the easiest Indian recipe I've ever made. If you want to make your first curry, this is a great beginner's recipe.

Indian Crockpot Coconut Chicken Curry
1 T butter
1 onion, roughly diced
1 heaping T minced garlic
2 t minced ginger
2.5 pounds skinless chicken thighs (bone-in or out)
3 T Sun curry powder (you can use another curry powder brand, but I can't promise the flavor balance will be as good, or you could make your own using this recipe, which is what I usually do: 1 T cumin, 1 t salt, 1 t coriander, 1 t turmeric, 3/4 t cayenne pepper (I like it spicy), 1/2 t cinnamon, 1/2 t cardamom, 1/2 t coarsely ground black pepper, 1 bay leaf, 1/2 t smoked paprika (optional), 1/2 t fenugreek (optional))
1 15 oz can crushed tomatoes or tomato puree
1 14 oz can coconut milk
I bunch cilantro (optional) (stems and leaves separated and chopped. Cook chopped stems in the slow cooker to flavor the dish; reserve chopped leaves for garnish.)
1 cup pumpkin puree (optional--to thicken)

Dump all ingredients except garnish in Crockpot in the order listed. Cook on low 6 hours or high for 3 hours. Garnish with chopped cilantro leaves if using.

UPDATE: I recently bought an Instant Pot, and have been having fun converting my recipes to work in it. Here's how to do it:
Using the Saute function, saute the onions, garlic, and ginger with the spices. Add remaining ingredients except pumpkin and stir together. Cover and close vent, then set to Poultry for 20 minutes. When finished, quick release and stir in pumpkin.

Serve with cauliflower "rice" or basmati.