In a food processor, combine all-purpose flour, kosher salt, and unsalted butter. Pulse until the mixture resembles coarse crumbs, about 30 seconds. Gradually drizzle in ice-cold water, pulsing until the dough begins to come together. Form it into a ball, wrap in plastic, and chill in the refrigerator for 1-2 hours. Once chilled, roll out the dough on a floured surface to fit your pie dish, then par-bake at 375℉ for 20 minutes, using pie weights to prevent puffing.

In a large mixing bowl, whisk together the apple butter, large eggs, dark brown sugar, and all-purpose flour until smooth. Stir in the vanilla extract and pour the sweetened condensed milk into the mix, blending thoroughly until fully incorporated. The filling should be creamy and uniform, rich with the sweet aroma of apple butter.

Carefully pour the filling into the pre-baked pie crust, ensuring even distribution. Place the pie in a preheated oven at 325℉ and bake for 40-45 minutes, or until the edges are set but the center remains slightly jiggly. Let the pie cool completely on a wire rack for about 3 hours, allowing it to set nicely.

While the pie cools, in a mixing bowl, whip together heavy whipping cream, powdered sugar, ground cinnamon, and a splash of vanilla. Use a hand mixer on medium speed until soft peaks form, indicating the whipped cream is light and fluffy.

Once the pie has cooled, spread the whipped cream evenly over the top. For an extra touch of sweetness, swirl in a few dollops of additional apple butter. Slice the pie and serve it with cinnamon whipped cream.