Spread bread cubes in two shallow baking pans. Melt 4 tablespoons of the butter and drizzle evenly over bread cubes; toss to coat. Bake, uncovered, in a 325 degrees F oven for 15 to 20 minutes or until lightly toasted, stirring once. Transfer to a very large bowl.

In a 12-inch skillet, melt the remaining 2 tablespoons butter over medium heat. Add squash. Cook, uncovered, for 5 minutes, stirring occasionally. Add celery and onion; cook, covered, 10 minutes more. Stir in 1/4 cup of the chicken broth. Cook, covered, 5 minutes more or until squash is just tender, stirring occasionally. Remove from heat. Stir in sage, parsley, nutmeg, salt, and pepper.

Add squash mixture to bread in bowl. Add 2 cups of the remaining broth; toss lightly to coat. Add enough additional broth to make a stuffing of desired moistness.

Transfer stuffing mixture to a greased 3-quart casserole. Cover and bake in a 325 degrees F oven for 30 minutes. Uncover and bake 15 to 20 minutes more or until stuffing is heated through. If desired, top with fresh sage sprigs. Makes 10 to 12 servings.

Make-Ahead Tip: Toast bread cubes and place in an airtight container at room temperature for up to 2 days.