Sift flour and sugar together in a large bowl. In a saucepan, combine cocoa, butter and water and bring to a boil. Pour over dry ingredients and add eggs, buttermilk, vanilla and soda. Pour into a greased 9×13 inch pan and bake for about 20 minutes. Let cool. Frosting: In a saucepan, add sugar, butter and milk. Bring to a boil for one minute remove from heat and whisk in chocolate chips, whisk until no lumps, then spread quickly over the cake. Do this quick it sets up really fast.