Whisk together all-purpose flour, kosher salt, and sugar in a mixing bowl. Cut in the cold unsalted butter until the mixture resembles pea-sized crumbs. Add ice-cold water and cider vinegar gradually, mixing until a dough ball forms.

Divide the dough in half, shape into discs, wrap in plastic wrap, and refrigerate for at least 1 hour.

In a large bowl, combine sliced fresh plums, halved figs, the sugars, potato starch, lemon juice, ground ginger, ground cinnamon, ground cloves, and Angostura bitters. Stir until all ingredients are evenly coated.

Roll out one disc of dough into an 11-inch round and line your pie plate, then refrigerate it for a few minutes. Roll out the second disc, cut it into strips for a lovely lattice topping. Fill the pie crust with the fruit mixture, arrange the lattice over the top, crimp the edges, and chill once more.

Preheat your oven to 425°F. Brush the crust with the egg wash and sprinkle with demerara sugar. Bake for 20-25 minutes until golden, then reduce the temperature to 375°F and continue baking until the juices are bubbling, about 30-35 minutes.

Remove the pie from the oven and cool on a wire rack for 2-3 hours to allow the filling to set.