Sorry to post a issue that TCP explains thoroughly, but I’ve tried the Mousseline Buttercream recipe twice, and I can’t get it right. Both attempts went wrong when beating the butter into the meringue:
First try: I added the butter tablespoon by tablespoon, and the icing got thin, then thickened, then became grainy. I followed Rose’s instructions to increase the beating speed until smooth again before continuing with the butter. This took about 4 minutes, deflating the egg whites and making the icing dense and buttery.
Second try: The icing got grainy at the same point in the process, but i only increased the speed a bit, lest I deflate the meringue again. The graininess didn’t go away, and I finished by folding it with a spatula to keep some air in. This produced a lighter texture than the first try, but less smooth.
Rose warned against the butter being too soft or too warm; in both tries my butter was cool, maybe a few degrees cooler than room temperature. Is it possible my butter was too cool? Also, I waited til the meringue was completely cooled down before adding the butter.
Please let me know what I might be doing wrong, and also if there’s a way to save my first two bathches, which have been sitting in the fridge since yesterday’s attempts.