Place flour and sugar in a large bowl, then sift and mix in cocoa powder, baking soda, cinnamon, and salt. Set aside. In a medium saucepan on high, melt and combine ½ cup butter, vegetable oil, and 1 cup Coca-Cola. Bring to a boil and remove from heat.
Preheat oven to 350 F. With a spatula, mix the Coca-Cola mixture into the flour mixture, then buttermilk and vanilla, then eggs. Pour batter into a greased 9x13-inch baking dish. Bake approximately 30 minutes or until toothpick comes out clean. Cool on wire rack.
While cake is still warm, prepare icing. Place the same saucepan over medium heat; melt ½ cup butter with ½ cup Coca-Cola and vanilla. Whisk until smooth, then remove from heat. Whisk in cocoa powder and powdered sugar 1/2 cup at a time until dissolved. Pour icing over warm cake. Allow to cool completely before slicing and serving.
Per serving: 260 calories, 9.5 grams fat (3.5 grams saturated fat), 26 milligrams cholesterol, 97 milligrams sodium, 44 grams total carbohydrates, 1 gram fiber, 2 grams protein.
