Preheat oven to 450°. Cut squash into 2-inch wedges; cut each wedge in half crosswise. (If using butternut, cut into smaller pieces.) Score a crisscross pattern 1/4 inch deep into squash flesh, using a sharp knife. Stir together melted butter and brown sugar until sugar dissolves. Brush one-third of butter mixture over all sides of squash. Place squash, flesh sides down, in a lightly greased aluminum foil-lined 15- x 10-inch jelly-roll pan. Bake at 450° for 10 minutes. Turn squash over; spread with half of remaining butter mixture. Bake 12 to 14 minutes or until tender. Remove from oven; increase oven temperature to broil. Brush squash with remaining butter mixture. Broil 2 to 3 minutes or until well caramelized. Sprinkle with salt and pepper to taste. Serve warm.