Make caramel glaze:
In a saucepan, add butter, brown sugar, cream or milk. Cook over medium heat, stir continuously, until the mixture comes to a boil.
DO NOT stir for 3 - 3 1/2 minutes. Remove from the heat and spread over the top of the cake. ( I line a cookie sheet with foil and remove my cake, for easier serving and so the caramel can run down the sides.)
Leave the cake sit for at least an hour before serving.