Collect all the necessary ingredients.
Melt butter and vegetable oil in a large skillet over medium heat. Add the chicken, onion, and garlic, cooking until the onion is softened and translucent, about 10 minutes. This step enhances the flavors, creating a savory base for the dish.
Add the tomato paste, curry paste, curry powder, tandoori masala, and garam masala, stirring until the mixture is smooth and free of lumps. This step ensures that the spices are well incorporated, creating a rich and flavorful sauce for the chicken.
Transfer the mixture to a slow cooker, then stir in the cardamom pods, coconut milk, and yogurt. Season with salt to taste. This combination creates a creamy and aromatic base that will infuse the chicken with rich flavors during the slow cooking process.
Cook on High for 4 to 6 hours or on Low for 6 to 8 hours, until the chicken is tender and the sauce has thickened to your liking. Before serving, be sure to remove and discard the cardamom pods. This slow cooking method allows the flavors to deepen, resulting in a rich, satisfying dish.