Yes, these red currant custard pastries can be made in advance, though the best approach is to prepare and bake them just before serving for optimal freshness. If you prefer to make them ahead of time, you can prepare the vanilla pudding and store it in the refrigerator for up to two days. You can also cut the puff pastry squares and assemble them with pudding and currants, placing them on a baking sheet, then cover and refrigerate until you are ready to bake them. When you are ready to enjoy your pastries, simply brush them with the egg wash and bake directly from the fridge. However, baked pastries are best enjoyed fresh; if you do need to store leftovers, keep them in an airtight container at room temperature for a day or two, although they may lose some of their flakiness over time. If necessary, reheat them in the oven briefly before serving to revive their crispiness.