Honeynut Squash Casserole with Sage Marshmallow Topping

Name: Honeynut Squash Casserole with Sage Marshmallow Topping
Ingredients: 5 pounds honeynut or butternut squash, peeled and cut into 1-inch chunks; 2 large eggs plus 4 egg whites, divided; 1 (12 ounce) can low-fat evaporated milk; 3 tablespoons packed light brown sugar; 2 tablespoons melted butter; ½ teaspoon ground cinnamon; 2 ½ teaspoons vanilla extract, divided; 1 ⅛ teaspoons salt, divided; 1 cup granulated sugar; ¼ cup light corn syrup; 2 tablespoons finely chopped fresh sage; ½ teaspoon cream of tartar