Odd, Ive never seen a Prailine topping on yams or sweet potatoes.
Fam still does the marshmallows or a candied version depending on who cooks.
Maybe that's an East coast thing?
I think you've probably had it, but I'm mis-speaking when I call it a praline topping. It isn't generally called that except around here. The recipes will say "pecan topping" or pecan crunch topping or pecan streusel or something like that. It's just that as a Texan, I know that if you cook down that sugar and butter, then stir in the pecans, you'll have pralines. This topping does somewhat "pralinize" in the oven.
Here are examples of the dish, random pics from the net: