Add the chicken pieces, onion, 4 minced garlic cloves, ginger, tomato sauce, heavy cream, 2 tablespoons butter, garam masala, cumin, turmeric, paprika, and 1 teaspoon salt to the slow cooker. Stir to combine everything evenly.

Cover and cook on low for 6 hours or on high for 3 hours until the chicken is very tender.

While the chicken cooks, make the naan dough. In a mixing bowl, combine the flour, baking powder, and 1/2 teaspoon salt. Stir in the yogurt until a soft dough forms. Knead briefly on a lightly floured surface until smooth.

Divide the dough into 4 equal portions and roll each into a thin oval or round shape.

Heat a skillet over medium heat. Melt the remaining 2 tablespoons butter and stir in the 3 minced garlic cloves. Cook each naan for 1 to 2 minutes per side until golden spots appear, brushing with the garlic butter as it cooks.

Stir the slow cooker sauce once more before serving. Garnish the butter chicken with chopped cilantro and serve alongside the warm garlic naan.