Put the marshmallows in the freezer and that's all! If you are freezing a lot of marshmallows, it's a good idea to divide them into small portions so that they won't stick together (although I don't bother).
You can eat them straight out of the freezer. They thaw quite quickly if left at room temperature, so you'll be able to separate the marshmallows easily.
Use these frozen marshmallows for cooking or baking.
I didn't know until after posting this that fellow Cookpad user "Kohe" uploaded a similar recipe (Recipe ID: 521552) long before I did.
Story Behind this Recipe
I froze marshmallows to keep them soft and tasty and to prevent them from going stale. I ate frozen marshmallows straight out of the freezer and they were delicious, so I posted this recipe.
If you store leftover marshmallows at room temperature, they'll become hard and unpalatable. This is a method to prevent marshmallows from becoming stale, but actually, I prefer them frozen. And the best thing about this is that you can keep them nice and tasty for months!