Make the Gluten-Free Pie Crust:
In a large bowl, whisk together the gluten-free flour, sugar, and salt.
Add the cubed butter and toss to coat in flour. Using your fingers, two forks, or a pastry cutter, work the butter into the flour until small pea-sized lumps form. If the butter starts to melt, refrigerate for 30 minutes.
Pour in 1/4 cup ice water and stir. Then mix in the sour cream. If the dough is too dry, add 1 tbsp water at a time until it forms a cohesive mass.
Split the dough into two pieces—one larger for the crust and the other for pie leaves. Wrap both in plastic wrap and chill for at least 1 hour.
Roll Out the Pie Dough:
After 1 hour, roll out the larger piece of dough on a well-floured surface. Ensure it’s large enough to fit a pie dish. Transfer to the dish, pressing the dough into the sides. Patch up any cracks with your fingers.
Tuck under the overhang and crimp the edges.
Prepare for Baking:
Separate one egg from the filling ingredients, saving the yolk for the filling. Brush the pie shell with the egg white to prevent a soggy crust. Freeze the shell for 15 minutes.
Preheat the oven to 400°F (200°C). Roll out the second piece of dough, cut leaf shapes using cookie cutters, and refrigerate.
Blind Bake the Pie Shell:
Place a sheet of parchment paper in the pie shell, fill with pie weights or dry beans, and bake for 15 minutes. Remove the parchment and weights, and bake for another 5-8 minutes until the crust is no longer raw. If the leaves are golden, remove them from the oven.
Make Cinnamon Sugar Topping:
Mix granulated sugar and ground cinnamon. Toss the warm pie leaves in this mixture and set aside.
Prepare the Apple Butter Filling:
In a large bowl, whisk together the apple butter, 2 eggs, 1 egg yolk, and brown sugar. Add the flour, cinnamon, salt, sweetened condensed milk, and vanilla. Whisk until smooth.
Fill and Bake:
Pour the filling into the cooled pie shell and sprinkle with the reserved cinnamon sugar mixture. Bake at 400°F for 10 minutes, then reduce the temperature to 350°F (175°C) and bake for 30-40 minutes until set.
Cool and Serve:
Let the pie cool at room temperature for 30 minutes, then refrigerate for at least 2 hours or overnight. Once chilled, top with whipped cream and enjoy!