Preheat the oven to 350°F (175°C).

In a mixing bowl, combine the flour and powdered sugar. Add the chilled cubed butter and mix until the mixture resembles coarse crumbs. Stir in the egg yolk and add ice water, one tablespoon at a time, until the dough comes together. Form into a disk, wrap in plastic wrap, and refrigerate for 30 minutes.

Roll out the chilled dough on a lightly floured surface to fit your 9-inch tart pan. Press the dough into the pan, trimming any excess. Prick the bottom of the crust with a fork and line it with baking parchment. Fill with pie weights or dried beans.

Bake the crust for 15 minutes, then remove the weights and parchment, and bake for an additional 10 minutes until lightly golden. Let it cool.

In a saucepan, heat the heavy cream and whole milk over medium heat until just simmering. Remove from heat and add the chopped dark chocolate. Let sit for 5 minutes, then whisk until smooth.

In a separate bowl, whisk together the eggs, granulated sugar, vanilla extract, and a pinch of salt. Gradually whisk in the chocolate mixture until fully combined.

Pour the chocolate filling into the cooled tart shell. Bake in the oven for 15 minutes or until the filling is set around the edges but still slightly jiggly in the center.

Allow the tart to cool completely at room temperature, then refrigerate for at least 2 hours before serving.

Serve the tart with a dollop of whipped cream or fresh berries for extra flavor.