Preheat oven to 350°F. Place squash cut side down in glass baking dish with 1/2 inch of water. Cover and bake 45 minutes or until tender. Uncover and turn squash halves cut side up. Season with salt and pepper.
Combine dried cranberries and hot water in small bowl. In a medium skillet, cook mushrooms over medium high heat until water mostly evaporates. Reduce heat to medium and add 3 Tbsp butter, onion and sage and sauté until beginning to soften, about 5 minutes. Add breadcrumbs and stir until crumbs brown lightly, about 3 minutes. Mix in cranberries with soaking liquid. Season to taste with salt and pepper.
Mound stuffing into squash halves. Dot with remaining 1 tablespoon butter. Bake until heated through and crisp on top, about 10 minutes.
Adapted from Bon Appétit, October 1995