In a large heat-proof bowl, mix all purpose flour and granulated sugar. Set aside.
2In double boiler, bring 1 stick of butter, vegetable oil, water and 1/4 cup cocoa to a boil. Stir well. Mix hot mixture into flour-sugar mixture. Add eggs, buttermilk, cinnamon, baking soda and vanilla extract. Mix well.
3Pour batter into a 9" x 13" pan which has been sprayed with non-stick cooking spray. Bake for 20-30 minutes or until it tests done. Let cool 5-10 minutes before icing.
4FOR THE ICING:
Sift together confectioners' sugar and 1/4 cup cocoa. While cake cools, in a double boiler, melt 1 stick butter. Add confectioners' sugar-cocoa to the melted butter and mix well. Slowly add about 6 tablespoons of milk for a smooth consistency. Pour icing evenly over partially cooled cake. Cool completely.