Put chopped apples in a large mixing bowl and toss with lemon juice. Whisk together the brown sugar, cinnamon, nutmeg, cornstarch and salt. Pour over apples and toss again. Spray a round baking dish (could use a 9 x 9 square dish) with cooking spray and pour in the apples. Sprinkle on vanilla extract and maple syrup. Cut butter up in small pieces over the apples. Put pie crust on and cut 3 slits in top. (I use a Pillsbury frozen pie crust but you could make your own).