Preheat the oven to 325˚F (160˚C).
Heat oil in a large Round French Oven over medium-high heat. Season chicken with salt and pepper. Working in batches, cook chicken until golden brown on all sides, 8-10 minutes per batch. Transfer to a plate.
Add butter and onions to drippings in pot; season with salt. Cook, stirring often, until onions are soft and golden brown, 10-15 minutes. Stir in garlic, ginger, curry powder and turmeric. Cook, stirring constantly, 2-3 minutes.
Add potatoes, chickpeas and chicken stock. Return chicken and any accumulated juices to pot. Add more broth if needed to cover chicken about three-fourths of the way up. Bring to a simmer. Cover pot and transfer to oven. Braise chicken until fork-tender, 55- 60 minutes.
Using Tongs and a Slotted Spoon, transfer chicken to a platter and cover with foil to keep warm. Add spinach to pot, cover, and remove from heat. Let stand until spinach is wilted, 5-7 minutes.
Stir yogurt into cooking liquid. Season with salt and pepper. Return chicken to pot. Warm over low heat (do not boil or yogurt may curdle).