Prep and preheat. Heat the oven to 375°F (190°C).
Place a rack in the lower third to help the bottom crust brown nicely.
Par-bake the crust. Line the pie shell with parchment and fill with pie weights or dried beans. Bake 12–15 minutes until the edges start to set. Remove weights and parchment, then bake 5 more minutes.
Cool slightly while you make the filling.
Mix the filling. In a large bowl, combine sliced apples with granulated sugar, brown sugar, flour, cinnamon, nutmeg, salt, lemon juice, and vanilla. Toss until the apples are evenly coated and glossy.
Make the crumble. In another bowl, whisk flour, brown sugar, granulated sugar, cinnamon, and salt. Cut in the cold butter with a pastry cutter or your fingers until pea-sized clumps form.
Stir in oats or nuts if using. Keep it chilled while you assemble.
Fill the crust. Pile the apples into the crust, mounding slightly in the center. Pour any juices from the bowl over the top—they add flavor.
Press down gently to reduce air pockets.
Add the crumble. Sprinkle the topping evenly over the apples, breaking it into various-sized clumps for texture. Brush the crust edge with milk or cream and sprinkle with coarse sugar if you like.
Bake. Place the pie on a lined baking sheet to catch drips. Bake 50–60 minutes, until the topping is deeply golden and the filling is bubbling in the center.
If the topping browns too fast, tent loosely with foil.
Cool properly. Let the pie cool at least 3 hours on a rack. This step is key—cooling allows the filling to set so your slices hold together.
Serve. Slice and serve at room temperature or slightly warm. A scoop of vanilla ice cream or a dollop of lightly sweetened whipped cream is a classic pairing.