My family was raised at the base of Woolverton Mountain in Arkansas (my maiden name was Woolverton). We would have Chocolate Gravy before we went to church every Sunday. Mother would make homemade biscuits and we would eat till the biscuits were gone. If we had left over Chocolate Gravy my mother would add an egg and turn it into Chocolate Pie. We loved Sundays. Company at the Hanna's house gets to enjoy it now.
Mix sugar, cocoa and flour in a medium saucepan. Stir in milk slowly whisking constantly. Continue stirring over medium heat until thicken. Take off heat and stir in butter and vanilla. Serve over hot biscuits (homemade, frozen or even canned).
Hope your family enjoys this as much as we did growing up in the 50's as well as today.