Use only pressed tofu, a product that is not water-packed, because it is very firm and dryotherwise, the filling will be too wet. Pressed tofu should be so firm that you can easily dice it or cut into thin strips. I have found pressed tofu in natural food stores and Asian markets, but if you cannot find it, use tempeh instead. You can make the pot stickers ahead and flash- freeze them for several weeks, or dust with cornstarch, wrap in plastic and refrigerate for several hours. Frozen pot stickers can be cooked after partial thawing.