Slow-cooker Indian Butter Chicken

Ingredients

• 3 pieces naan bread
• 1 red onion, halved and thinly sliced
• 1 pound baby red-skinned potatoes, halved or quartered if large
• 1 fresno chile or red jalapeno pepper, halved lengthwise, seeded and sliced
• 1 small bunch cilantro, leaves and tender stems separated, chopped
• 1 1/2 pounds skinless, boneless chicken thighs (about 6)
• 1 tablespoon garam masala
• kosher salt and freshly ground pepper
• 2 tablespoons unsalted butter, cut into pieces
• 1 cinnamon stick
• 1 15-ounce can tomato sauce
• 1/2 cup heavy cream
• kosher salt