I just made a shortening based "champagne" buttercream using a moscato reduction.
does anyone know what kind of longevity this will have and storage (shelf or fridge) is best?
If this is made from shortening, sugar, reduced wine, flavours it will be OK on the shelf.
But I would not leave it out for more than a day or so on the cake. If you have leftovers then refrigerate or freeze them as for any other delicate flavoured food.