If you bake a tart and want to keep it in the fridge for a couple of days, the filling may soften the crust.  In order to avoid this, you can cover the cooled crust with melted chocolate using a pastry brush. This will make a barrier between the filling and the crust. This will also make your dessert extra delicious. You can see me doing this step in my fruit cookie cups. Alternatively,  you can remove your crust from the oven, wait for a couple of minutes so it will be warm and cover the crust with egg white using a pastry brush. Then put it into the oven and let it dry for a couple of minutes. This will also work as a barrier.