Preparation Preheat oven to 350°F. Place squash, cut side down, in 13x9x2-inch glass baking dish. Pour water over squash. Bake until skin on squash is blistered and brown and flesh is tender, about 1 hour 15 minutes. Turn squash cut side up. Cool slightly. Scoop out flesh and transfer to medium bowl, leaving 1/3-inch-thick shell. Mash flesh. Add butter and stir until melted. Season to taste with salt and pepper. Spoon squash back into shells. (Can be prepared 1 day ahead. Cover and refrigerate. Rewarm in 350°F oven until heated through, about 30 minutes.) Sprinkle squash with chopped walnuts and serve.
Preparation Preheat oven to 350°F. Place squash, cut side down, in 13x9x2-inch glass baking dish. Pour water over squash. Bake until skin on squash is blistered and brown and flesh is tender, about 1 hour 15 minutes. Turn squash cut side up. Cool slightly. Scoop out flesh and transfer to medium bowl, leaving 1/3-inch-thick shell. Mash flesh. Add butter and stir until melted. Season to taste with salt and pepper. Spoon squash back into shells. (Can be prepared 1 day ahead. Cover and refrigerate. Rewarm in 350°F oven until heated through, about 30 minutes.) Sprinkle squash with chopped walnuts and serve.