In a food processor, combine all-purpose flour and kosher salt, pulsing until mixed. Add cold, cubed unsalted butter and pulse until the mixture resembles wet sand. Gradually pour in ice cold water, one tablespoon at a time, until a shaggy dough forms. Divide the dough into two discs, wrap in plastic, and refrigerate for 1-2 hours.

Preheat your oven to 375°F (190°C). Roll out one chilled dough disc on a floured surface to fit a 9-inch pie plate. Place it in the dish, crimp the edges, and dock the bottom with a fork. Line with parchment paper, fill with pie weights, and bake for 15 minutes. Remove the weights and parchment, then bake for another 5 minutes until lightly golden.

Lower the oven temperature to 325°F (163°C). In a large mixing bowl, whisk together the apple butter, large eggs, dark brown sugar, all-purpose flour, and vanilla extract until smooth. Slowly stir in sweetened condensed milk to create a creamy filling. Pour this mixture into the warm, par-baked crust, ensuring an even distribution.

Place the pie in the oven and bake for 30 minutes. After this time, shift the pie to the bottom third of the oven and continue baking for an additional 10-15 minutes. The filling should be set but slightly jiggly in the center—avoid overbaking.

Once baked, remove the pie from the oven and let it cool on a wire rack for at least 3 hours. For quicker cooling, refrigerate the pie.

While the pie cools, make the whipped cream. In a mixing bowl, whip the heavy cream until it begins to thicken. Gradually add powdered sugar, ground cinnamon, and a splash of vanilla extract. Continue whipping until soft-stiff peaks form.

Once the pie has cooled completely, generously top it with the cinnamon whipped cream. Optionally add dollops of apple butter on top before serving.