The dough is either too dry or too cold. If it crumbles, add a few sprinkles of water into it but try to handle as little as possible. If it just cracks at the edges when you run the rolling pin over it, it probably just needs to warm up a little. Allow it to sit on the counter for a few minutes. You do not want it to get too warm, however, or the crust will not come out flaky.
Be sure to chill the dough at least one hour before trying to roll it out. Lightly flour your working area as well as the top of the dough. If you constantly run into this problem and are not using a pastry cloth, perhaps you would want to invest in one. They are not expensive and truly are a tremendous help rolling all types of dough. Most pastry cloths will come with a rolling pin cover. This combination will help with all the sticking problems and is well worth the investment. Pastry cloths are made from thin cotton. You do still need to lightly flour the cloth and the cover before using them.
Try placing your pie on the bottom oven rack. Begin baking the pie at a high temperature (425° to 450° F.), then reduce the heat after 20 minutes or so. The initial high temperature will help the crust to brown while reducing the temperature will allow the filling to cook thoroughly before the crust burns.
Before you pour your filling into your pie crusth, brush the bottom of it with beaten egg whites or if you wish, heated jelly. You could also try baking the crust prior to pouring in the filling. Alternatively, you could partially bake it prior to pouring in the filling, however, this can be difficult if you are making a double-crust pie. Many cooks find it helps to make a lattice top crust in this instance. What you will need to do, is use beaten egg to help seal the top crust to the partially baked bottom crust, because you do not have the two crusts to pinch together as you do with a full top crust.
Before you begin to roll your dougn AND after rolling the dough, allow it to "rest" in the refrigerator. In addition, while you are fitting the dough into your pie pan, do your best not to pull or stretch the dough. This should prevent the dough from shrinking. When you have the crust placed into the pan, use a fork and poke the crust in several places. This allows any steam to escape which, in turn, prevents the crust from puffing up. Now we come to the "but"! If you are baking a custard pie where the filling is baked in the crust (as opposed to a cream pie, where the filling is cooked on the stove top then poured into a pre-baked crust) do not poke holes in the bottom crust, or the custard will seep through the holes. Instead, you can use weights in the bottom of the crust to keep it in place: either pie weights, which are specifically made for this purpose, or dry beans or rice. Be sure to line the crust with parchment paper or foil before putting in the weights.
The first and easiest solution to this would be to increase your oven temperature. You can also brush the top crust with beaten egg or milk for a glossy look. Just be sure to do this before you cut steam vents in the top crust or you will seal them shut. If the ingredients in your crust include vinegar or lemon juice, that could be your problem as well. To counter-attack any negative effect to your crust from these ingredients, add about 1 teaspoon of sugar to your dry ingredients before you mix in the fat. Vinegar and lemon juice prevent browning.
Consider investing in some pie crust shields. These truly do wonders. You can use strips of foil if you wish, but it can be difficult to get that foil to stay put where you want it to! The pie crust shields are so easy to use and should pretty much solve this problem for you. About 20 minutes before the end of baking time, remove the shield or foil if you are using it and allow the edges to brown to perfection.
This is where minimal mixing comes into play. When liquids are incorporated into the flour, it begins to create gluten. The more this gluten forms, the tougher the crust will be. If you over-mix your dough, you are helping it form more gluten, you don't want that! In addition, the above tip regarding lemon juice and vinegar can apply here as well.
Be sure you use your fat ingredient after it is thoroughly chilled. If you have any liquids in your recipe, chill those as well. When you rub your fat into your flour, you should do so until it has a sandy texture and some larger pieces as these will separate the layers while slowly melting during cooking. This process is what makes a crust flaky. To create a crust both flaky and tender, use half chilled butter and half room temperature shortening. Leave the butter in pieces about the size of a pea.
This is where the steam vents are so important. When the fruit is cooking it emits steam. If this steam has no place to go, it leaks! (And makes one heck of a mess in your oven! I know, I did it with blueberries once!). If you did remember your steam vents and are still experiencing some leaking, it could be because the filling is very sweet and sugary. In this case, the filling bubbles up which in turn, seals the vents shut. Finally, some leakage may be unavoidable. Protect your oven by covering a baking sheet with foil and setting the pie on top of it.
Most often this means you cooked your pie too long. You could either increase your oven temperature or cut your fruit into larger pieces..
This can happen when the fruit loses water volume, in the form of steam, as it cooks. To prevent the gap, partially cook your filling before putting it into your pie crust. If you do try this however, you will need to use more fruit than your recipe requires. Place the fruit into a large saucepan along with the remaining filling ingredients. Cook over a low heat until your fruit is softer and loses some volume. Next, fill your pie and bake at a higher temperature. Cover it loosely with foil during the first part of baking so the top crust does not burn.
This is usually an indication your eggs became too hot in custard or cream pies. Tempering eggs helps with this problem. To do this, place your eggs into a bowl; whisk them thoroughly. Slowly pour about a cup of the heated pie ingredient mixture into the whisked egg(s) and whisk constantly. This will gently warm your eggs. Next, slowly whisk this mixture into the saucepan containing the rest of the milk mixture. Another thing that can cause curdling is if your recipe ingredients does not include any type of starch and you bring the mixture to a boil. It is a good idea to always put into practice constant stirring of your filling while it is on the stove. If none of this helps solve your problem, try using a double-boiler for cooking your cream filling.
For fruit fillings, use cornstarch, tapioca flour, arrowroot, or all-purpose flour to thicken it up. Depending on the juiciness of the fruit, use about 1/4-cup all-purpose flour, or 2-tablespoons cornstarch, tapioca flour, or arrowroot. For cream fillings, cook the filling long enough after adding your eggs. If your eggs were not cooked long enough, your filling can break down after it cools. Cook and stir the mixture for at least two full minutes after you whisk the eggs in to it. If you have an instant pudding filling, serve it within a few hours. Instant pudding will separate and get watery if allowed to sit for too long. If you want filling with more staying power as well a richer, creamier taste, use cook and serve pudding, or make the filling from scratch.
You can freeze a fruit pie raw or baked. To prepare an unbaked frozen pie,
do not defrost it first. Preheat the oven to 400° F. and bake for about
50 to 60 minutes. Cut steam vents in the top crust. To prepare a baked
frozen pie, allow it to thaw at room temperature for an hour, then bake it
at 375° for 30 to 40 minutes, until heated through. Freezing custard or
cream pies is not a good idea.