I'm a beginner baker, do the odd sponge cake and cupcakes with DS but seem to struggle with buttercream. I know, it's ridiculous. I have a few different recipes for buttercream but always seem to get the same end result. It's too runny! I always make sure the butter isn't too warm and the cakes are completely cold before I start piping/spreading. I even put it in the fridge to firm it up which works great until I put it in an icing bag and it just slops on the cake. What am I doing wrong?