Marinate the Chicken:
In a bowl, mix yogurt, lemon juice, garam masala, cumin, chili powder, turmeric, and salt. Add chicken pieces, toss to coat, and refrigerate for at least 30 minutes (or overnight for deeper flavor).
Layer in Crockpot:
Place the marinated chicken into the crockpot. Add onion, garlic, ginger, tomato sauce, tomato paste, paprika, cinnamon, butter, and olive oil. Stir gently to mix.
Slow Cook:
Cover and cook on Low for 6–7 hours or High for 3–4 hours, until the chicken is tender and cooked through.
Add the Cream:
Stir in the heavy cream (or coconut cream) and brown sugar. Mix well and let cook uncovered for 15–20 minutes to thicken slightly.
Serve:
Garnish with chopped cilantro and serve hot with rice or naan bread.