If you have to pre-bake a pie for some function or another, chances are the crust will get a little soggy by the time you serve it. Luckily, pastry genius Stella Parks has a blindingly elegant solution: Magnesium sulfate. Photo by Sanickels.
You are most likely familiar with magnesium sulfate in some capacity or another. If you've studied chemistry, you know it as the stuff that lined the desiccator and kept your reagents from absorbing water. (You also remember the "desiccator" as that scary expensive thing that you would break if you didn't slide the top off the right way.) If you didn't study chemistry, you probably know of magnesium sulfate as "bath salts" or "Epsom salts".
Just as it did in chemistry class, magnesium sulfate absorbs water from its surrounding environment, and we can harness that for the good of pie crusts everywhere. It's a pretty simple process. First, get some food-grade, unscented Epsom salts and dry them out completely. (Parks walks you through the process in the link below.) Once they are "bone dry", transfer them to an air-tight container and place your cooled pie (in its plate) directly on top of the salts, allowing it to stay as fresh as possible until it makes it to the picnic (or office party, or wherever the heck you're taking it).
How to Combat Soggy Pie Crusts With Epsom Salt [Serious Eats]