Sift together the T65 flour, unsweetened cocoa powder, and powdered sugar in a mixing bowl.
Cut the cold butter into small cubes and mix into the dry ingredients using your fingers or a pastry cutter. The texture should resemble coarse crumbs.
Add the egg yolks and vanilla extract (if using) and gently mix to form a dough. Add a tablespoon of water if the dough is too dry.
Form the dough into a rectangle, wrap in plastic wrap, and refrigerate for at least 30 minutes.
Preheat the oven to 180°C (350°F) while the dough chills.
Once chilled, remove the dough and slice it into thin sticks. Arrange them on a baking sheet lined with parchment paper.
Bake for 12 minutes, or until the sticks are golden brown and crisp. Let them cool completely.
While the sticks are cooling, melt the dark chocolate in a double boiler or microwave. Stir until smooth.
Once cooled, dip each stick into the melted chocolate, allowing any excess to drip off. Optional: Sprinkle chopped nuts or sea salt on top before the chocolate sets.
Allow the chocolate to firm up before serving. Enjoy!