Getting very sharp corners on a square cake with buttercream. Any advice would be soooo greatly appreciated!
Stiff buttercream, hot bench scraper!
When applying/smoothing the icing onto the sides with your scraper, it's best to avoid doing one side at a time by removing your scraper from the side's surface as you get near the end. Try turning the corner (without lifting your scraper) all in one swipe while pushing the extra icing from one side on to the next side at the corner to help build it up rather than allow it to rip cake/crumbs away. I hope this makes sense.
If you can't ice it smooth the first time, it's also helpful to just cover with a light crumbcoat then chill in the refrigerator. Your second coat will be so much easier to apply and turn the corners after chilling without fear of breaking off the corners.
There are some videos on YouTube that will show you how to do it way better than I can explain it. That's how I learned to do it, and I'm still practicing.
I LUV doing square cakes! Here are some photos on how I do it.