1. In a small bowl, combine the warmed milk and 1 teaspoon of the sugar. Sprinkle the yeast over the milk and stir lightly. Let stand until foamy, about 5 minutes.
2. In the bowl of a standing mixer fitted with the paddle, combine the flour, cocoa, salt, ground Sichuan peppercorns, chocolate chips and the remaining 3 tablespoons plus 2 teaspoons of sugar and mix well. With the machine at medium low speed, beat in the yeast mixture. Add 6 of the eggs, one at a time, scraping down the side of the bowl as necessary. Reduce the speed to low and beat in the butter, 1 tablespoon at a time, until thoroughly incorporated; scrape down the sides of the bowl a few times. The dough should be soft, smooth and slightly sticky.
3. Transfer the dough to a floured bowl, cover with plastic wrap and let stand in warm place until risen and puffy, about 1 hour.
4. On a floured work surface, pat down the dough. Gather it into a ball. Flour the bowl and return the dough to it. Cover and let stand again until risen, about 45 minutes.
5. Generously butter two 9-by-4½-inch loaf pans. Turn the dough out onto a floured work surface and cut it in half. Pat each half into a 9-by-8-inch rectangular loaf and transfer both loaves to the prepared loaf pans, seam sides down; neatly fold in the ends. Loosely cover with plastic wrap and let stand until the dough fills the pans, about 1 hour.
6. Preheat the oven to 350°. Beat the remaining egg and brush some over the tops of the loaves. Using a sharp knife, make a lengthwise slice in the center of each loaf. Bake for 35 minutes, rotating the loaves halfway through baking, until they sound hollow when tapped. Transfer the pans to a rack to cool slightly, then run a knife around the edges and turn the loaves out onto the rack. Serve the brioche warm or at room temperature.
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