Chocolate Fudge Frozen Upside-Down Cake
["2 c. flour", "1/4 c. cocoa", "4 tsp. baking powder", "1/2 tsp. salt", "1 2/3 c. sugar", "1 c. chopped walnuts", "1 c. milk", "1/4 c. butter", "1 oz. semi-sweet chocolate, melted"]
["Butter a 9 x 13-inch cake pan.", "Preheat oven to 350\u00b0.", "Mix flour, cocoa, baking powder, salt and sugar.", "Add chopped walnuts. Warm milk and butter together; whisk into dry ingredients.", "Beat well.", "Add melted chocolate; beat well.", "Pour into pan and level the top.", "Drizzle with sauce."]
["flour", "cocoa", "baking powder", "salt", "sugar", "walnuts", "milk", "butter", "semi-sweet chocolate"]