Turkey Zuppa Toscana

Name: Turkey Zuppa Toscana
Ingredients: 1 pound ground Italian sausage; 0.5 cup unsalted butter; 1 pound leftover cooked turkey, pulled; 0.5 cup turkey drippings; 3 tablespoons minced garlic; 1 tablespoon ground thyme; 1 tablespoon dried parsley; 1 tablespoon mustard powder; 2 teaspoons salt; 1 teaspoon ground black pepper; 3 cups water; 3 russet baking potatoes, unpeeled and cubed; 8 ounces white mushrooms, quartered; 1 medium white onion, halved and sliced; 8 ounces chopped kale; 8 ounces sour cream; 1 cup milk