Peel and cut squash into cubes. Boil until tender, about 5 to 7 minutes, and drain. Brown onion, garlic, and parsley in 2 tablespoons butter seasoned with salt and pepper. Soak bread in ice water and wring out; chop fine. Add to onion and garlic mixture; cook, stirring, for 2 to 3 minutes. Add drained squash and cook 2 to 3 minutes more, stirring. Remove from heat. Beat egg and add, allowing it to absorb into the mixture. Season with salt and pepper, if needed.
Place in casserole dish or baking pan. Cover top with cracker crumbs and dot with remaining butter. Bake for 20 to 25 minutes, until the crumbs brown.