Toss the walnuts, gorgonzola, thyme, chopped apples, and maple syrup together in a medium size bowl. As you are working with the apples (chopping them, mixing them in with the other ingredients), if you want, you can squeeze a little lemon juice on them to help keep them from discoloring. Cover the mixture with plastic wrap while you prepare the crust.

Preheat oven to 350°F. Roll out pastry dough to 13-inches, at an 1/8 of an inch thickness. Place pastry dough on a rimmed baking sheet. (Rimmed because the pastry will leak butter during the cooking process.) Mound the filling in the middle of the rolled out dough, and spread out evenly to 1 1/2 inches to 2 inches from the edge of the dough. Pleat the edges of the dough over the filling.

Bake for 45 minutes to an hour, until crust is nicely browned. If at any time it looks like the walnuts are getting a little burnt, you can lightly tent a piece of aluminum foil over the center. 

Remove from oven and let cool for 10 minutes before serving. A pizza wheel works great for slicing up the tart.