Whenever you make a tart using phyllo (filo) dough, I have found that it's best to have a filling that is not too juicy. The dough has little fat, and moisture can make it soggy. When you work with phyllo, think of working with those colored tissue sheets; they both have the same thickness. You can always patch and piece the dough, but make sure you always butter in between any layer or patching piece.
PIES AND TARTS RECIPE HELP / LOW / REDUCED-FAT RECIPE HELP

INGREDIENTS
2 large golden delicious apples, peeled and cored and cut into 1/2-inch slices
2 tablespoons dark brown sugar
1 teaspoon fresh lemon juice
1/2 teaspoon ground cinnamon
Canola Oil spray or 3 tablespoons melted butter, cooled to tepid
Eight 12- x 17- inch sheets phyllo (filo) dough thawed overnight (available from the grocery store)

NOTE: For best results, thaw frozen filo dough overnight in the refrigerator. If thawed at room temperature, the sheets tend to stick together. Filo dough dries out quickly and can crack when exposed to air. Keep the stack of filo sheets covered with plastic wrap or a damp cloth, and work quickly as the sheets are removed from the stack. Filo dough can be refrozen, as well.

INSTRUCTIONS
Position a rack in the center of the oven and preheat to 375 degrees F. Lightly spray a nonstick baking sheet with canola oil or cover with parchment paper.

To make the filling, in a medium bowl, toss the apple slices, brown sugar, lemon juice and cinnamon. Set aside.

Place 1 sheet of filo dough on a prepared baking sheet and very lightly spray it with canola oil (or you can brush with melted butter). Top with the other filo sheets, lightly spraying each sheet with oil (or brush with melted butter), and progressively arranging the sheets across each other at angles to form a sunburst pattern. Mound the apple filling in the center. Bring up the filo sheets to completely cover the filling.

Spray the top of the filo with oil (or brush with butter).

Bake until the filo is deep golden brown, about 35 minutes. Cool on the baking sheet on a wire cake rack for 10 minutes. Slide the tart on a serving platter. Serve warm.

The Healthy Oven Baking Book, by Sarah Phillips, Doubleday, 1999