on that stale piece of bread that has run out and only does for croutons. And in a very simple and inexpensive way: with simple ice cubes!!
Rub an ice cube on the surface of the bread, until its crust becomes slightly moist!! Then put it in the oven at 180ᵒ C, for 12 about minutes and your bread will be as if it has just come out of the oven (the original one!!).
You will get the same result if you wrap your bread in aluminum foil, (no ice cream this time) and put it in the oven.
And if you want to keep it fresh for longer, store in a cupboard at room temperature, and your bun is preserved 6 times more than,what if you had put it in the fridge!!