Step 1: Marinate the Chicken (Optional, but Recommended)

1. Prepare the Marinade: In a large bowl, combine ½ cup yogurt, 1 teaspoon garam masala, ½ teaspoon ground cumin, ½ teaspoon paprika, and a pinch of salt.
2. Add the Chicken: Add the chicken pieces to the marinade, coating them thoroughly. Cover and refrigerate for at least 1 hour, or overnight for maximum flavor. This step helps tenderize the chicken and adds depth to the flavor.

Step 2: Prepare the Slow Cooker Base

1. Sauté Onion, Garlic, and Ginger: In a skillet over medium heat, melt 1 tablespoon of butter with the vegetable oil or ghee. Add the chopped onion, and sauté for 4-5 minutes until softened. Add garlic and ginger, and cook for an additional minute until fragrant.
2. Toast the Spices: Add garam masala, ground cumin, ground coriander, turmeric, paprika, and cayenne pepper to the skillet. Stir continuously for about 1 minute until the spices are fragrant. This helps release the full flavor of the spices.
3. Add Tomato Puree: Pour the tomato puree or crushed tomatoes into the skillet, stirring well to combine with the onion and spices. Allow the mixture to simmer for 5-7 minutes to develop a rich base.

Step 3: Assemble the Slow Cooker

1. Transfer to Slow Cooker: Pour the tomato-spice mixture into the slow cooker. Add the marinated (or plain) chicken pieces, coating them thoroughly in the sauce.
2. Add Remaining Butter and Cream: Add 3 tablespoons of butter, cut into pieces, and pour in the heavy cream (or coconut milk for a dairy-free option). Stir well to incorporate.
3. Season with Salt and Pepper: Add salt and black pepper to taste, then stir everything together one final time.

Step 4: Cook the Butter Chicken

1. Set the Slow Cooker: Cover and cook on low for 6-8 hours or on high for 4 hours. The chicken should be tender, and the sauce thickened and creamy.
2. Adjust Consistency if Needed: If the sauce is too thick, you can add a bit more cream or water. If it’s too thin, let the slow cooker cook uncovered for the last 30 minutes.

Step 5: Final Seasoning and Serve

1. Taste and Adjust: Taste the butter chicken and adjust the seasoning with additional salt, pepper, or garam masala if desired.
2. Garnish: Serve the butter chicken over basmati rice or with naan. Garnish with chopped cilantro, a squeeze of fresh lemon juice, and an optional drizzle of cream or yogurt for extra richness.