In a pot, add the butter and set it over medium low heat. Once it has melted, add the brown sugar and whisk.

Let it cook for a couple of minutes, you’ll see it bubble as if it’s boiling and give it quick whisk then add the milk and whisk it in.

Cook it with the milk for another 2 minutes, this time without stirring. You’ll see bubbling again. Turn off the heat and add the nut butter, salt and vanilla - whisk it quickly.

Add half of the sugar and whisk until you can’t see any more bits of powdered sugar, then add the other half and whisk again until you have a thick, smooth but very runny ‘frosting’.

Pour over your prepared bars/brownies/blondies or cake and let cool completely. It’ll seem like it’s going to be a mess but trust - after about an hour it’s going to thicken and solidify enough for you to be able to slice it.