How To Get Crisp Square Corners on a Cake
By the talented: BKeith

OK, mini-demo on square corners. This was done rather quickly, so forgive the imperfection. You ought to be able to get the technique, anyway.

1. First, a square "cake" (sorry -- didn't have a real cake around to mess with). Slapped some icing on a square pan, and when I went to clean some icing away, I came up with a perfect square corner without even trying.

So I took an intentional swipe at the corner to mess it up a bit so you could see what's what.

2. With your left hand, hold a spatula vertically in front of you so the right edge of the spatula is where you want the corner to be

3. With another spatula in your right hand, start adding dabs of icing on the side of the cake running away from you, building up the corner against the "dam" spatula in your left hand.

4. Now gently slide the left hand spatula to the left, slowly bringing it away from the cake side to minimize the lift-off mark

5. Once the corners are built, I generally go back with my bench scraper and clean up the sides between the corners.