Slow Cooker Butter Chicken

INGREDIENTS

• 2 tablespoons butter
• 2 tablespoons vegetable oil
• 4 large skinless, boneless chicken thighs, cut into bite-sized pieces
• 1 onion, diced
• 3 cloves garlic, minced
• 2 teaspoons curry powder
• 1 tablespoon curry paste
• 2 teaspoons tandoori masala
• 1 teaspoon garam masala
• 1 (6 ounce) can tomato paste
• 15 green cardamom pods
• 1 (14 ounce) can coconut milk
• 1 cup plain yogurt
• salt to taste