I will be using the following recipe as a filling for some cupcakes. Would they need to be refrigerated? I prefer not to as they dry up the cupcakes and harden the buttercream icing.
Unfortunately, this filling does need refrigeration, because of the raw egg whites. In regular marshmallow recipes, the eggs are cooked, so there's less of a problem. I wonder if there's any way to substitute powdered egg whites or meringue powder for the raw egg whites? I guess it would depend on whether those things will whip up like egg whites (and how much of either one of those powders and how much water you would have to use to get the equivalent amount of egg white).
Why don't you just make IMBC without adding the butter? Before you add the butter you basically are making a soft marshmallow.