If you’re looking for a frosting that doesn’t harden and stays satiny smooth then swiss meringue buttercream might be for you. It’s not very sweet and it’s VERY buttery so it might be more appropriate for those people who scrape the frosting off their cupcake just to eat the cake (yes there are people who do that, they are usually old). I tried this out on both my grandparents and my parents who are all guilty of the discarded frosting offence and they all loved it.
It’s a bit of a faff but it is worth it if you have these sort of restrictions to bear in mind.
150g egg whites (about 5 eggs worth)
250g caster sugar
340g butter, cooled and cubed
pinch of salt
1tsp vanilla extract (for a vanilla version)
Heat the egg whites and sugar in a bowl over a pan of simmering water, until the egg whites get hot to the touch and the sugar has dissolved. Whisk constantly to ensure it all dissolves.
Leave the bowl to cool slightly and then in a scrupulously clean mixing bowl, add the egg white and sugar mixture and begin to whisk on high speed until thick, white and glossy. It can take ages so be patient, about 5-10 minutes is usually right.
Once your meringue mix is stiff and the bowl is cold, start to throw in cubes of butter, whisking on medium speed until you have incorporated it all.
It’s A LOT of butter, and it seems like too much but carry on going and all of a sudden the mixture goes from meringue with random flecks of butter to the SMB texture you’re after.
If it’s too runny or curdles, pop it in the fridge for 10-15 minutes and then re-whip it. It SHOULD be fine though.