Marinate chicken pieces in yogurt, chicken masala, turmeric powder, and salt for 4 hours.
Puree garlic, ginger, onions, and green chilis into a paste.
Heat peanut oil in a pan and roast the curry paste.
Add the fenugreek, cardamom, cloves, and cumin seeds. Continue roasting.
Add the butter.
Add tomato paste and roast for a minute.
Add the cream.
Brown chicken pieces in a separate pan.
Combine chicken and butter sauce.
Transfer to the slow cooker and cook for 6 hours on low.