Preheat oven to 350 degrees. In large mixing bowl, beat eggs; add sugar, 1/2 cup at a time. Add melted cup of butter; beat until frothy. While beating, add flour, cocoa and cinnamon. Add vanilla and beat until well mixed. Stir in nuts, if desired. Pour into greased and floured baking dish. Bake at 350 degrees for 20 to 25 minutes. Cool before cutting. For a variation, replace 1/2 cup cocoa with 1/2 cup kahlua and bake as before.