This is the best icing (which I prefer to heavier frostings) recipe for the stuff my Mom used to make when I was growing up.  She usually put it on her No Egg Chocolate Cake (popular also in the 50's), and we also loved penuce candy over the holidays.  Penuce candy is tricky to make but this icing is not - it's fairly easy, just keep stirring.

https://chocolatewithgrace.com/brown-sugar-icing/