Make the Crust:

1. In a large bowl, whisk together flour, sugar, and salt.

2. Cut in the cold butter using a pastry cutter or your fingers until pea-sized crumbs form.

3. Add the egg yolk and gradually mix in cold water, 1 tablespoon at a time, just until dough comes together.

4. Shape into a disc, wrap in plastic, and refrigerate for at least 1 hour.

5. Roll out the chilled dough and press it into a 9-inch pie dish. Trim and crimp the edges.

6. Blind bake at 375°F (190°C) for 15 minutes with pie weights, then remove weights and bake 10 more minutes. Let cool.

Make the Filling:

1. In a saucepan over medium heat, combine chocolate, milk, cream, and butter. Stir until melted and smooth.

2. In a separate bowl, whisk together cornstarch, cocoa powder, cinnamon, cayenne, and salt.

3. Add eggs, egg yolk, vinegar, and vanilla to the dry mixture and whisk until smooth.

4. Slowly pour the warm chocolate mixture into the egg mixture, whisking constantly.

5. Pour filling into the pre-baked pie crust.

6. Bake at 325°F (165°C) for 30–35 minutes, or until the center is set but still slightly jiggly.

7. Let cool to room temperature, then chill for at least 2 hours.

8. Dust with powdered sugar before serving.