In a large skillet, over medium heat, combine butter and light brown sugar until combined. Add apple slices, lemon juice, cinnamon, nutmeg, and salt. Toss apples and coat evenly with the sugar mixture. In a small bowl, combine granulated sugar and flour. Pour mixture over apples. Add vanilla. Cook over medium heat for 5-8 minutes until apples begin to soften and juices thicken.
Remove from heat and transfer apple filling to a large bowl. Allow the mixture to cool down to room temperature.
Preheat oven to 400°F.
Line a 9-inch pie pan with half the pastry. Turn apple mixture into the lined pie plate. Top with remaining pastry, as desired. Trim and flute the edges. Make sure there are slits in top crust to allow steam to escape.
Prepare an egg wash by mixing the egg with milk. Brush egg wash over the pie. Sprinkle with turbinado sugar.
Bake for 35 to 40 minutes or until golden brown. Remove from oven. Serve warm or at room temperature. Cover and refrigerate leftovers.
We left the skins on our beautifully colored apples but apples may be peeled, if desired.
To give shine to the crust, an egg wash or cream wash is recommended. For an additional layer of flavor and texture, sprinkle Turbinado Sugar over the pie.