Final answer:
Puff pastry is chilled overnight to solidify the fat for distinct layering and to allow gluten to relax, which prevents shrinkage and toughness for optimal flakiness and tenderness.
Step-by-step explanation:
There are two primary reasons why puff pastry is chilled overnight. First, the chilling process solidifies the fat within the dough, which helps maintain distinct layers of fat and dough. This separation is crucial for achieving the desirable flakiness in the baked puff pastry as it ensures that when the pastry is baked, the water in the fat evaporates and pushes the layers apart, creating the puff. Second, refrigerating the dough overnight allows the gluten in the dough to relax. This relaxation prevents the pastry from shrinking or becoming tough when baked. For an optimal, flaky, and tender puff pastry, a cold and rested dough is essential.