4 Tbsp butter or ghee
4 onions, minced
6 cloves garlic, minced

2 Tbsp ginger powder
2 Tbsp paprika
2 Tbsp turmeric

4 tsp cumin powder
4 tsp ground mustard
2 tsp cayenne pepper (For medium heat. Add or reduce by ½ tsp if desired.)
2 tsp cinnamon
1 tsp ground cloves
1 tsp salt

4 Tbsp white vinegar
4 Tbsp tamarind paste
4 tsp lemon juice

2 cup tomato sauce (or passata)
2 ½ cup water

3 pounds skinless, boneless chicken breasts (or thighs) cut into bite size chunks
2 Tbsp tandoori masala (optional)

1. Melt a few tablespoons of butter in a skillet over medium heat. Stir in onion and cook slowly until the it caramelizes to a dark brown, about 15 minutes.
2. When the onions are almost done, add the garlic and cook for a couple more minutes. Stir in all the spices and saute for another minute.
3. Transfer onion mixture to a blender. Add everything else, except water, chicken and tandoori masala. Blend until smooth.
4. Transfer the sauce to a pot. Add the water to the blender and blend to clean it, add to the pot. Simmer for about 45 minutes.
5. Toss cubed chicken breast with tandoori masala and spread out onto a baking sheet.
6. Bake chicken at 375 until no longer pink in the center, about 12 minutes.
7. Once the chicken is cooked, add it to the sauce. (This can be added during the simmering time.)