cooking pastry for bottom of pie using cold filling
There are two techniques (that I know of) that will help you. I often use both...


A thin layer of fat on the inside (the "top of the bottom") will prevent the water from the filling from soaking into the crust and allow the crust to 'cook through'. I use butter but shortening, lard or cooking oil will do.
Par baking with pie weights will allow the crust to begin cook
before the filling is added.


I don't know if this helps with 'cooking properly' or not, but I use vodka to replace half of the water to mix the dough. This inhibits the production of gluten and makes a 'flakier' crust. (based on a tip from Alton Brown specifically for apple pie, but it works all around...)