Strudels are one of the great dishes of central Europe, especially in the countries that made up the former Austrian empire. In their homelands, they're made with fruit of all kinds or even savory cheese-based fillings, though the apple version is best-known here. Strudels can be made up in advance and frozen before baking, to provide a quick and easy dessert on another occasion.
You can use two different kinds of pastry to make strudels. The traditional central European dough is paper-thin, rather like Greek phyllo pastry. Phyllo's an easy substitute if you don't have the time or energy to make your own from scratch. Alternatively, you can use puff pastry as the wrapper, as many Germans do. Both types of pastry freeze beautifully and bake well straight from the freezer, so there's no practical reason to choose one over the other. Go with whichever you prefer.
The best-tasting strudels have a good balance of sweet and tart apple flavor, just like the best apple pies. Choose an apple, such as a Cortland or Braeburn, that hits that balance and holds its shape as it cooks and softens. Most recipes have you toss the apples with flour, starch or breadcrumbs to soak up any excess moisture. If you're making strudels for freezing, add a little extra, because the apples will shed some juice when they thaw. Roll up your apples in phyllo or fold them in puff pastry, as directed in your recipe.
If you've made your strudels with phyllo, you can help them hold their shape in the freezer by rolling them in parchment paper. Wrap each strudel individually with plastic wrap. Puff pastry strudels don't need a parchment layer, but can be wrapped carefully in plastic or placed in large freezer bags. To freeze the strudels, place them on a cookie sheet or in a flat plastic container and freeze them in a single layer. Once they're frozen, pack them into a plastic tub or place them on their own shelf to prevent damage as you rummage through the freezer for other items.
It's best to bake your strudels right from the freezer, because if you thaw them first the juices will make your pastry soggy. Preheat the oven as directed in your recipe. If you used puff pastry that will often be 400 degrees Fahrentheit or higher, while phyllo can bake perfectly well at 375F or lower. The goal is to have crisp and perfectly golden pastry, while the apples cook and become tender. You might have to reduce your heat late in the cooking process or cover the pastry with foil to keep it from getting too dark. Brush the crust a few times with the juices that run from the strudel, to create a flavorful caramelized glaze.