In a food processor, combine all-purpose flour and kosher salt. Cut the unsalted butter into small pieces and pulse until the mixture resembles coarse crumbs, about 10-15 seconds. Gradually add very cold water, pulsing until the dough starts to come together but is still shaggy. Shape into a disk, wrap in plastic, and refrigerate for 1-2 hours to firm up.

On a lightly floured surface, roll out the chilled dough into a circle about 12 inches wide. Carefully fit the rolled dough into a 9-inch pie plate, pressing it gently against the edges. Freeze the crust for 15 minutes, then dock the bottom using a fork to prevent bubbling. Line with parchment paper, fill with pie weights, and bake in a preheated oven at 375°F for 20 minutes until lightly golden.

In a large mixing bowl, whisk together the apple butter, large eggs (at room temperature), dark brown sugar, all-purpose flour, and pure vanilla extract until the mixture is smooth and well combined. Ensure there are no lumps for a perfect custard texture.

Pour the smooth apple butter filling into the pre-baked pie crust. Bake in the oven at 325°F for 30-45 minutes, until the edges are set and the center is slightly jiggly. Allow to cool completely on a wire rack.

While the pie cools, prepare the cinnamon whipped cream. In a mixing bowl, combine heavy whipping cream, powdered sugar, ground cinnamon, and a splash of vanilla extract. Beat the mixture on medium-high speed until soft peaks form, about 3-5 minutes.

Once the Apple Butter Pie is completely cool, dollop the freshly made cinnamon whipped cream generously on top. For an added touch, swirl in a bit of apple butter to create a marbled effect.