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1
Spray a large bowl with vegetable cooking spray, dampen a clean kitchen towel with water, and set aside.
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2
Sprinkle the yeast over the water in the bowl of an electric mixer fitted with the dough hook attachment, and let stand for 10 minutes, until the yeast begins to foam.
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3
Add the flour, cocoa powder, 2 teaspoons of the salt, and 1/2 cup of the sugar to the bowl, and mix on low speed. Add 7 of the eggs and mix the dough until it comes together in a ball, about 5 minutes. Add the butter and mix until well combined. The dough will be very soft and sticky. Transfer the dough to the prepared bowl, cover with the damp towel, and let rise in a warm place until the dough doubles in volume, about 1 hour.
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4
With your fist, punch down the dough, then let it rise again in the refrigerator until doubled, at least 2 hours, or overnight.
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5
Spray the sides and bottom of two 9 x 5 x 3-inch loaf pans with vegetable cooking spray and set them aside.
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6
Punch down the dough and divide it into 2 pieces of equal size. Work with one piece of dough at a time, leaving the other covered. Slightly flatten each piece of dough and fold its corners toward the center to create rounded edges. Invert the dough on your work surface so that the seams are down. Cup the dough in your hands. Keep your fingers close together, your thumb resting on your forefinger, to form a rounded shape. Make a slight back-and-forth movement with your wrists so that the dough rotates in between your fingers. Use your fingers to make the dough roll around in the tight cradle that they form. Your hands should never lift from the table as you perform this circular motion. The dough will shape into a tight ball. Repeat with the other piece of dough.
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7
With your fingers, stretch each ball into a rectangle about 9 inches wide and 10 inches long (they should be as wide as the loaf pans are long). Sprinkle half of the chocolate chips over each rectangle of dough. With the width of the dough parallel to your work surface, roll each rectangle over itself lengthwise, to form a cylinder. Shape the dough into a loaf by rolling its bottom edge toward the top. The ends of each loaf should be tapered when the proper shape is achieved. Roll the dough over so that its seam is at the bottom, and slightly taper the dough further on both ends if necessary. Place the loaves in the prepared pans, seam side down, and lightly dust them with a little bit of flour. Place the pans in a warm place and let the dough rise until it fills three quarters of the pans, about 1 hour.
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8
Place a rack in the center of the oven and preheat the oven to 350u00b0F.
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9
Prepare an egg wash with the remaining egg by whisking it very well with the pinch of salt and pinch of sugar, until the mixture is well blended. Brush the tops of the loaves with the egg wash, and with a sharp knife, slit their tops lengthwise. Bake for 30 to 40 minutes, rotating once during baking, until the brioche has a shiny golden brown top, and a wooden skewer inserted into the center comes out clean. To be sure, pull the breads out of their molds and tap the bottoms: if they sound hollow, they are done. Unmold the loaves and let cool on a wire rack.
