Preparation Steps

• Make the tangzhong: whisk 1/2 cup milk and 2 tablespoons bread flour together in a small saucepan over medium-low heat. Stir constantly until the mixture thickens to a smooth paste that clings to the spoon, about 2–3 minutes. Remove from the heat and let it cool to room temperature (about 20–30 minutes).
• Mix the dough: In the bowl of a stand mixer fitted with the dough hook, combine 4 cups bread flour, sugar, yeast, and salt. Whisk briefly to blend. Add the cooled tangzhong, the two eggs, warm milk, and vanilla. Start the mixer on low and mix until a rough, slightly sticky dough forms, about 5–7 minutes.
• Incorporate the butter: Cut the softened butter into small pieces. With the mixer running on medium-low, add the butter a few pieces at a time, waiting for each addition to be incorporated before adding more. Continue kneading 10–12 more minutes until the dough is smooth, elastic, and stretches thinly without tearing (windowpane stage). The dough should feel tacky but not sticky.
• First rise: Transfer the dough to a lightly oiled bowl, cover tightly with plastic wrap or a damp towel, and leave in a warm spot until nearly doubled in size, about 1 hour 45 minutes. If your kitchen is cool, this may take a bit longer.
• Add the chocolate: Turn the risen dough out onto a lightly floured surface and gently press it flat into a rough rectangle. Sprinkle the chocolate chips over the center third, fold the dough over the chips, and roll gently several times to trap and distribute them without shredding the dough. If chips tend to clump, you can fold and rest the dough for 10 minutes and finish distributing.
• Shape and braid: Divide the dough into three equal pieces. Roll each into a long rope about the length of your loaf pan. Place the three ropes side by side, pinch one end together, and braid tightly. Tuck both ends under to create a neat loaf.
• Second rise: Grease a 9 x 5-inch loaf pan and set the braided loaf inside. Loosely cover and let it proof in a warm place until puffy and nearly doubled, about 45–60 minutes depending on room temperature.
• Preheat the oven to 350°F (175°C). Whisk the egg for the wash until smooth and brush gently over the top of the loaf. If the braids are very tall, you can tent the loaf loosely with foil halfway through baking to prevent over-browning.
• Bake: Place the pan on the middle rack and bake 30–35 minutes, or until the top is deep golden brown and a skewer inserted into the center comes out clean or with just a few moist crumbs. If the top is coloring too quickly, cover loosely with foil for the last 10–15 minutes.
• Cool and serve: Let the brioche cool in the pan 10–15 minutes, then transfer to a wire rack to cool another 30 minutes before slicing. Warm slices toast beautifully.