Spiced Grapefruit Upside-Down Cake
["1 grapefruit", "1/3 c. butter or margarine", "1/2 c. brown sugar, packed", "18 walnut halves", "1 (16 oz.) pkg. pound cake mix", "2 eggs", "milk (as needed for mix)", "1 tsp. cinnamon", "1/8 tsp. ground cloves", "1 c. whipping cream", "2 Tbsp. powdered sugar", "1/2 grapefruit peel, grated"]
["Heat oven to 325\u00b0.", "Finely grate about 1/2 grapefruit peel; reserve.", "Peel and cut grapefruit into 6 cartwheels and drain well."]
["grapefruit", "butter", "brown sugar", "walnut", "pound cake mix", "eggs", "milk", "cinnamon", "ground cloves", "whipping cream", "powdered sugar", "peel"]