Prep chicken: Pat chicken dry and season lightly with salt and pepper.
Sauté aromatics: In a skillet, heat oil and lightly sauté onions, garlic, and ginger for 2–3 minutes until fragrant. Optional: This step adds depth of flavor.
Combine ingredients in slow cooker: Add chicken, sautéed onion mixture, tomato puree, butter, garam masala, cumin, coriander, turmeric, chili powder, salt, pepper, and sugar/honey. Stir to combine.
Slow cook: Cover and cook on low for 4–6 hours or high for 2–3 hours until chicken is tender and cooked through.
Add cream: Stir in heavy cream or coconut cream and cook on low for an additional 15–20 minutes to heat through.
Serve: Garnish with fresh cilantro. Serve hot with naan bread for dipping.