1. Blind Bake The Crust
Blind baking is really just another way of saying "pre-baking." It simply means that you bake the pie crust on its own before adding the filling. This is something you do if the filling itself isn't going to be cooked (like a fruit tart) or if the filling will cook faster than the crust (like with a quiche). You can also either fully bake the crust or partially-bake it so that it has a head start when the full pie goes in the oven. The recipe should specify how far to cook the crust.
There are two ways to go about blind baking:
A. Docking involves pricking the crust with a fork to allow steam to escape evenly. Otherwise the crust will tend to bubble up and cook unevenly.
B. Pie weights do the essentially same thing by pressing down the crust and holding it in place. You can buy fancy ceramic pie weights or simply use dried beans. Either way, put a layer of parchment between the crust and the pie weights to keep the pie from picking up any off flavors from the weights, and push the weights all the way to the edges to help keep the sides from collapsing during baking.
For either method, bake the pie crust in a 425° oven until the edges are brown and golden. Allow 20-30 minutes for full baking or 10-15 minutes for partial baking. If you're using pie weights or beans, remove them halfway through cooking so the steam can escape and the bottom can fully cook.
2. Thickening The Fruit Filling
Cornstarch vs. quick-cooking tapioca or flour:
A. Cornstarch has a nice smooth texture and no real flavor, but it can lead to an occasional murky color with berry pies and its thickening power is compromised with high acidity fruit like cherries.
B. Quick-cooking tapioca will never result in a cloudy filling and soaks up really juicy fruit better than anything. However, it's a little difficult in the sense that it really needs high heat to activate completely. Make sure to give your pies a good ten minute dose of heat at 400 F if you're using this thickener.
C. Flour is an easy thickener in that you generally always have it on hand and it works beautifully. It can lead to a gummy, cloudy filling with delicate summer berries though. Reserve using flour as a thickener for heartier fruits like apples and pears.
3. Pay Attention To Bake Times
One reason you'll often end up with a runny fruit pie is simply that it hasn't been baked long enough. Any thickener you use needs a little time to set up, and people often see their crust turning light brown and think the pie is done when it's really not. I always cover the fluted edge of my pie crust with a strip of aluminum foil to keep it from getting to brown, especially since it's whole grain it tends to be darker in color to start with.
4. Prepare Your Fruit
Let your fruit sit in sugar for a half an hour and drain the natural juices that will gather. This is especially good to do with peaches or strawberries. I also cook my fruit especially apples, or pears since they shrink down so much. I place them in a skillet and cook with no moisture they will give off moisture until they have become tender. I add all my spices and sugar if needed. Then I add the precooked fruit to the partially blind baked crust.
5. Soak Up The Juice
Try sprinkling graham cracker crumbs inside your bottom crust; they soak up some of the juices released from fruit during baking. I have also used ground cookie crumbs on the bottom of the crust before adding the fruit.
A couple of other baking tips are place your pie pan on a cookie sheet and in the lower 1/3 of the oven. I also always cover the edge of the crust up front with a long piece of aluminum foil so it does not get to brown. Fresh fruit pies are summers great gifts, so get into the kitchen and surprise your family with a pie.