I need to make some cream puffs to serve in big batches, and I will need to fill the cream puffs ahead of time before actually serving. Is there an ingredient that I can add that will work to keep the cream puff shells crispy for several hours? I notice that my cream puffs tend to be soft after 1 hour of filling. I have found that Big Papa's cream puffs do remain crispy after several hours of filling.
Cream puffs (also known as choux buns) are small buns made from choux pastry that are filled with whipped cream or a custard filling. We suspect that you may actually be referring to Papa Beard's cream puffs (Papa Beard's is a Japanese bakery chain with franchises worldwide). Unfortunately their cream puffs are quite difficult to emulate as they are made from a base of choux pastry but are then covered in a shortcrust-type pastry (pie shell).
We can offer a couple of tips to try and help to keep your cream puffs from softening too much, though once filled most choux will soften as it will absorb moisture from the filling. Once you have baked the cream puffs we suggest that you split them in half and remove any damp pastry from the centre with a teaspoon. You can then return the pastry shells to a low oven for 5 minutes so that they have completely dried out. Store the puffs in an airtight container for up to 2 days and re-crisp them in a low oven for 5 minutes on the day you intend to use them (let them cool before filling).
For the filling we suggest you use a creme patissiere rather than just whipped cream. You can find plenty of creme patissiere recipes on-line. Whilst UK double cream is quite stable once whipped, whipping cream in other countries (such as heavy cream in the US) tends to separate and "weep" if it left to stand which will make it easier for the pastry to become soft. As creme patissiere is thickened with eggs and cornflour (cornstarch) it is more stable and will weep less, though if the puffs need to stand for any length of time and it is a warm enviromnent then they will need to be refrigerated. You could also fill the bottom half of the cream puffs and then just add the tops at the last minute, which should keep the tops crisp and is probably a good option if you do need to refrigerate the filled puffs.