You are here: Home » Recipes » Barley Casserole Barley Casserole Recipe by Relish ContributorKitchen Tested Yield 6 to 8 servings Serve this rich but wholesome-tasting side dish in place of rice for a change. PrintEmail Ingredients 1 cup medium barley1 envelope onion soup mix4 cups water1 tablespoon light stick margarine1/2 pound fresh mushrooms, sliced Instructions Preheat oven to 350F. In a 3-quart casserole dish, combine barley, onion soup mix and water. In a small skillet, melt margarine over medium-low heat and saute mushrooms until tender, about 5 minutes. Add to barley mixture. Cover with a lid or tightly with foil and bake 1 to 1 1/4 hours, or until barley is done and liquid is absorbed.