In a mixing bowl, whisk together 200 g of flour, 100 g of granulated sugar, 40 g of cocoa powder, and ¼ teaspoon of salt until well combined.

Cut in 120 g of cold butter using a pastry cutter until the mixture resembles coarse crumbs.

Add 1 egg and 1 egg yolk to the mixture, and mix until a dough forms; wrap the dough in plastic wrap and refrigerate for at least 30 minutes.

Preheat your oven to 180°C (350°F). This ensures your tart shell bakes evenly.

On a lightly floured surface, roll out the chilled dough to fit into a 9-inch tart pan.

Transfer the rolled-out dough into the tart pan, pressing into the edges and trimming any excess.

Bake the crust for about 15 minutes, or until firm and slightly set. Allow cooling.

In a saucepan, heat 400 ml of milk over medium heat until just below boiling.

In a separate bowl, whisk together 4 egg yolks, 80 g granulated sugar, and 40 g of flour until smooth.

Slowly pour hot milk into the egg mixture while whisking constantly to temper the eggs.

Pour the combined mixture back into the saucepan and cook over medium heat, stirring continuously until thickened.

Stir in dark chocolate until melted completely into the filling.

Pour the filling into the cooled tart shell and refrigerate for at least 30 minutes to set.