Brioche Dough

1. Rehydrate the dry yeast in warm milk and let it sit for about 5 minutes.
2. In the bowl of a stand mixer fitted with the dough hook, combine the flour, powdered sugar, and salt. Mix on medium speed.
3. Add the melted and cooled butter, egg yolks, and the milk with the yeast. Knead for about 5 to 7 minutes until a smooth ball of dough forms.
4. Cover the bowl with a cloth and let the dough rise at room temperature for 1.5 to 2 hours, or until it doubles in size.
5. Place the dough on a floured surface and punch it down to release the air. Divide the dough into 4 equal balls, and roll each out on parchment paper into large discs about 1/8 inch (3 mm) thick.

Chocolate Filling

1. In a small bowl, combine the chopped chocolate, butter, brown sugar, and powdered sugar. Microwave for 1-2 minutes until melted and smooth, stirring occasionally.

Assembly

1. Place the first disc of dough on a baking sheet lined with parchment paper.
2. Spread a layer of chocolate filling over the entire surface, then cover with a second disc of dough.
3. Repeat this step two more times, finishing with the fourth disc on top.
4. Trim the edges by cutting a round shape using a large plate, approximately 10 inches (25 cm) in diameter.
5. Lightly press the center with a glass or small bowl to mark it. Cut the dough into 4 pieces, leaving the center intact.
6. Then, cut each piece in half again to create 8 pieces, and repeat until you have 16 strips.
7. Twist each strip about 2 times in opposite directions, then pinch the ends together to seal. Let the dough rise for another 30 minutes to 1 hour.

Baking

1. Preheat the oven to 347°F (175°C). Brush the dough with the remaining egg white using a pastry brush. Bake for about 20 minutes, or until the brioche is puffy and golden brown.
2. Let it cool slightly, sprinkle with confectioner's sugar, and serve.