What is a par baked pie crust?

You can get my instructions along with my all buttah recipe here, towards the base of the recipe (step 6):

https://food52.com/recipes/24928-all-buttah-pie-dough

Par-baked means "partially" baked. In this case, the pie crust is baked until it is nearly done, about 80% - not fully baked. This helps prevent a soggy bottom pie. You can cover the raw dough with parchment and weigh it down with beans or pie weights, or if you have a second dish the same size, you can use that as a weight instead. In the case of using a second dish, you can also bake your crust upside down- that is, bottom of filled pie dish facing upwards. That particular trick also helps prevent shrinkage, because the crust is being pulled towards the rim of the plate, instead of the bottom. And it's easy to monitor the baking progress.

Par baked means the crust is pre-cooked before the filling goes in. To par-bake, put a piece of parchment paper inside the crust and fill it with dried beans or pie weights. This makes sure the crust stays up and intact during par-baking.