The following delicious recipe is courtesy of Ellen Vidalakis Furgis and D. Eugene Valentine, and is excerpted from their book Greek Cooking at Its American Best.
Triangles, or Tyropitakia
One of the most common finger-foods in Greece, tyropitakia vary according to available cheeses and the mood of the cook (the mageiros or mageirissa). Feta, mizithra, or manouri cheeses are usually preferred, with grated kasseri, kefalotyri, or Parmesan supplementing either the amount or the taste. Soft ricotta, cottage cheese, and cream cheese help mitigate the saltiness and sharpness of the Greek cheeses.
The pastry (called filo, Greek for "leaf") is available in Greek, Middle Eastern, and some Italian stores in 1-pound packages. If the filo is frozen, defrost it according to the directions on the box, which require that the pastry be left in the airtight plastic wrapping so it will not dry out. Filo dries quickly and crumbles after it is opened, so cover it with a smooth, damp kitchen towel (not the Turkish type) to keep it at a workable consistency. Should you tear one of the sheets while you're working with it, use it between whole sheets. Do not try to patch it together with water; it will become pastry and sticky. Finally, the secret to the successful use of filo is butter. Do not let your parsimony or calorie consciousness intrude here! If you skimp on the amount you use, or skip spreading it on some of the sheets, your pastry will emerge sodden instead of flaky and crisp. (Yields about 90 triangles)