Lamb Pot Roast with Oranges and Olives

Name: Lamb Pot Roast with Oranges and Olives
Ingredients: 1 4–5-pound boneless lamb shoulder; Kosher salt, freshly ground pepper; 6 garlic cloves, thinly sliced; 2 mandarin oranges or tangerines, unpeeled, thinly sliced into rounds; 1 cup Taggiasca or other fruity, brine-cured black olives, pitted, coarsely chopped; 2 tablespoons chopped fresh savory or rosemary; 1 teaspoon crushed red pepper flakes; 1 1/2 cups beef stock or low-sodium chicken broth; 1 1/2 cups dry red wine; 1 cup tomato purée