1 (4- to 5-pound) side of lamb ribs or lamb breast
Kosher salt and freshly ground black pepper
1 1/2 teaspoons smoked paprika
1 1/4 teaspoon ground cumin
1 teaspoon ground coriander seed
1/2 teaspoon ground fennel seed
1/2 teaspoon sugar
1/4 teaspoon red chili flakes
1 1/2 cups homemade or store-bought low-sodium chicken stock
1 tablespoon whole grain mustard
1 tablespoon unsalted butter
Preheat oven to 300°F. Season ribs all over with salt and pepper. In a small bowl, thoroughly combine smoked paprika, cumin, coriander, fennel, sugar, and chili flakes. Rub ribs all over with spice mixture and place on a wire rack set in a rimmed baking sheet or roasting pan.
Bake ribs for 1 hour, then increase heat to 375°F and cook until browned outside, tender within, and an instant-read thermometer registers 175°F, about 1 hour longer. Let rest for 10 minutes.
Meanwhile, pour off fat from pan. Set pan on burner and heat over medium heat. Add 1/2 cup stock and stir, scraping up any browned bits; pour into a medium saucepan and add remaining 1 cup stock. Cook over medium heat until reduced by half, about 8 minutes. Stir in mustard and season with salt and pepper. Off the heat, whisk in butter.
Divide ribs by cutting between the bones and serve with the sauce.