Place the all-purpose flour and salt in a large bowl. Add butter and use your fingers to break the butter into the flour until mixture resembles small peas. Whisk egg yolk with 1/4 cup cold buttermilk in a small bowl and then add the egg mixture to the flour mixture. Mix with a wooden spoon, drizzling in more buttermilk as needed (no more than 1 tablespoon at a time), until dough just comes together (a few dry spots are ok). Gently knead dough on a lightly floured surface until no dry spots remain, about 1 minute. Divide dough in half. Shape each piece into a circular disk.
Grease an 8-inch pie plate.
Roll out 1 disk of dough onto a lightly floured surface to a 12-inch round (reserve the other round of dough for another use, you do not need it for this recipe). Carefully transfer the crust to the prepared pie plate. Lift up the edges and allow the dough to sink down into the dish. Trim edges to even out crust if needed, then prick the bottom of the dough with a fork a few times. Cover the pie plate and place in the fridge for at least 1 hour or up to two days.
Preheat the oven to 350 degrees F.
To make the pumpkin pie filling, mix together the pumpkin, heavy cream, brown sugar, egg, pumpkin pie spice, salt and vanilla in a mixing bowl until combined. Pour the mixture into the bottom of your chilled pie crust.
To make the pecan pie filling, cream together the sugar and butter until combined. Add one egg at a time, scraping down the sides if needed until the eggs are fully incorporated. Add the maple syrup, salt, vanilla and bourbon until combined. Stir in half of the pecans.
Carefully spoon the pecan pie over the pumpkin filling. Some of the two filling will mix, this is OK, but try your best to be careful with the pecan filling so you will get two layers of pie! Once you have added all of the pecan pie filling to the crust, sprinkle on the remaining pecans and chocolate chips (if using).
Place the pie in the middle rack of the oven and bake for 45-55 minutes or until the center just has a little jiggle to it. If the top of the pie is burning before the center is done, cover with foil. Allow the pie to cool completely before serving. Sprinkle with flaky sea salt. Store in the fridge and bring to room temp before serving if desired.
*To make you own pumpkin pie spice, mix together 1 teaspoon cinnamon, 1/4 teaspoon ginger and an 1/8 teaspoon nutmeg.