The user is making Serious Eats' Pasteis de Nata and has prepared the custard one day ahead. The recipe states the custard can be made up to three days in advance. The question is whether to bring the custard to room temperature or heat it before pouring it into the pastry shells. The recipe does not explicitly address this. The dough preparation involves several steps of kneading, chilling, and folding with butter. The syrup is made by boiling sugar, water, and aromatics to a specific temperature. The custard is made by thickening milk, cream, and cornstarch, then incorporating egg yolks and the syrup, and finally straining. The dough is then sliced, and each piece is pressed into tins to form shells. These shells are then refrigerated. Finally, the custard is poured into the chilled shells and baked. The recipe specifies that the dough portions should be allowed to warm to room temperature for 15 minutes before being pressed into the tins. This is described as important for achieving a flaky edge. However, there is no instruction to heat or cool the custard before pouring. Given the custard is cooled completely after preparation, it would likely be used at room temperature or slightly chilled. Since the recipe doesn't mention warming the custard, it's implied it should be poured in its cooled state. The pastry shells are chilled before filling, suggesting a temperature contrast might be beneficial for puffing. Therefore, pouring the cooled custard into the chilled shells is the most logical next step based on the recipe's instructions.