Help! My Swiss Meringue Buttercream is soupy.
Once you add your butter, your stiff peaks will disappear and your mixture may appear thin and runny. This is ok. It may mean that your eggs were still slightly warm and/or your butter was too warm. Try whisking for a few more minutes and you may find your mixture will eventually come back together on its own. If it doesn’t, place your bowl in the fridge for 20 minutes to let the mixture firm up slightly and whisk again.