To start it's important to use a good quality non-stick pan or a very well-seasoned cast iron pan. Tofu will stick if the pan isn't preheated well (make sure it's very hot), and if there isn't enough oil/vegan butter. This shouldn't be a problem with this recipe because quite a lot of butter is used. If you used less than the recipe calls for though that could be a contributing factor. Also once the tofu squares are in the pan, don't touch them for a few minutes. It's important to wait until a golden crust is formed. Then they will release much easier when it's time to flip.