Add the tomato sauce, garlic, ginger, cumin, garam masala, smoked paprika, turmeric, chili powder, salt, and honey to the crockpot. Stir until the sauce is evenly mixed.
Add the chicken thighs and turn them until they are coated in the sauce.
Scatter the cold, chopped butter over the top of the chicken.
Cooking
Cook on low for 4 to 6 hours or on high for 2 hours, until the chicken is cooked through and tender.
Remove the chicken from the crockpot and place it on a cutting board to cool slightly.
Add the heavy cream to the crockpot and whisk until the sauce is smooth and creamy.
When the chicken is cool enough to handle, cut it into bite-sized pieces and return it to the crockpot. Stir to coat the chicken in the sauce.
Serving
Serve with basmati rice and garnish with the chopped fresh parsley.
Notes
For an even creamier sauce, you can add the heavy cream towards the last 30 minutes of cooking. Adjust the chili powder to your spice preference. Refrigerate leftovers for up to 4 days or freeze for up to 3 months.