Babka can be made with a variety of fillings, from a simple cinnamon-sugar mixture to the nut-chocolate mixture here. If the brioche dough is too sticky to work with at any point during the shaping process, cover and refrigerate for 20 to 30 minutes to help it firm up.

Prepare the dough for:

Refrigerate the dough for 1 hour. Stir together in a small bowl:

Set aside. Prepare and set aside:

Have ready:

Transfer the dough to a lightly floured work surface. Roll it out into a roughly 20 × 10-inch rectangle and spread evenly with the cocoa-butter mixture. Sprinkle evenly with the chopped chocolate and walnuts. With a long edge closest to you, roll up the dough into a cylinder. Slice the cylinder in half lengthwise to expose the layers of filling. Twist the two lengths of dough around each other to form a simple braid shape, then fold the braid in half and place in a generously buttered 9 × 5-inch loaf pan. Brush the loaf with:

Sprinkle with the streusel, cover, and let rise until puffy and increased in volume, 1 to 1 ½ hours.

While the loaf is rising, preheat the oven to 350°F.

Bake the babka until golden brown, 50 to 55 minutes. Let cool in the pan on a rack for 15 minutes, then use a thin offset spatula to help release it from the pan. Let cool completely on a rack.