Sweet Potato Gratin with Homemade Raspberry Nectar

Name: Sweet Potato Gratin with Homemade Raspberry Nectar.
Ingredients: For the Raspberry Nectar; • 24 ounces fresh raspberries (or thawed if frozen); • 1 cup granulated sugar; • Pinch of kosher salt; • 2 tablespoons lemon juice; For the Gratin; • 2 cups homemade Raspberry Nectar; • 3 cups homemade or low-sodium prepared chicken stock (broth); • 6 tablespoons unsalted butter; • 1 1/2 teaspoon kosher salt; • 1/2 teaspoon ground or a 1 1/2-inch stick cinnamon; • 1/2 freshly ground black pepper; • 5 1/2 pounds long orange-colored sweet potatoes, peeled and thinly sliced; • 1 pint fresh raspberries for garnish