My husband’s grandmother makes a Chocolate cake with chocolate frosting. The frosting turns hards after putting on cake. I think it’s a pretty old recipe. Thanks inadvance for your help.
The cake you are refering to is a Chocolate Cake With Hard Fudge Icing, and yes it is pretty old. It is in one of the Better Homes & Gardens Cookbooks from the late 60’s/early 70’s. This cake also happens to be my wife’s favorite, and my mother-in-law has a copy of the book (we just made one for her birthday last week). I will be more than happy to copy the recipe down and share it with you. I will be seeing her today so hopefully I’ll have it posted for you this afternoon 
Joe Slate