Dice the chicken small so it cooks quickly and fits better inside the pastry. Do not overfill the pastries or they may burst open while baking. Cool the chicken filling slightly before assembling so the puff pastry stays cold and flaky. Keep the puff pastry cold while working with it. If it gets too soft, place it back in the fridge for a few minutes. Drain excess liquid from the chicken filling if needed. Too much moisture can make the pastry soggy. Use parchment paper so the bottoms do not stick. Bake until deeply golden since underbaked puff pastry can look done outside but stay doughy inside.