Bad folding techniques

When cooking dumplings, including pierogi, one of the most common mistakes is trapping excess air when folding them. Always try to get the feeling as close to the seal as possible when sealing pierogi. If you don't, any trapped air will expand during the cooking process and cause the dumpling to burst open.

Before you start sealing your pierogi, dampen one-half of the circumference with a wet finger or a wet paper towel. This should aid in the formation and maintenance of an effective seal (via Tasting Poland). Then, fold your dough disc in half to form a half-moon shape. Begin pinching the pierogi closed from the center of the edge and work your way to one corner, taking care not to trap air as you go. Then, pinch the other half of the pierogi closed. Some people like to make a more decorative secondary seal by twisting and repressing the first seal to make it look braided.