Slow Cooker Indian Butter Chicken

Ingredients

• 2 lbs boneless, skinless chicken thighs (cut into bite-sized pieces)
• 1 large onion (finely chopped)
• 4 cloves garlic (minced)
• 1 tablespoon ginger (freshly grated)
• 1 tablespoon garam masala
• 1 tablespoon ground cumin
• 1 1/2 teaspoons ground turmeric
• 1 teaspoon chili powder
• 1 teaspoon ground coriander
• 1 teaspoon paprika
• 1 1/2 teaspoons salt
• 1 can (15 oz) tomato puree
• 1 1/4 cups heavy cream
• 1/4 cup unsalted butter (cut into pieces)
• 1 tablespoon sugar
• 1/4 cup fresh cilantro leaves (chopped, for garnish)
• Cooked basmati rice or naan (for serving)