This chocolate babka will make you swoon! Soft brioche bread ribboned with rich dark chocolate, and topped with a crumbly chocolate streusel.
Place the flour, water, yeast, sugar, salt, eggs, and egg yolk in a large mixing bowl and mix on low speed (with a dough hook attachment) for 6 to 8 minutes, stopping halfway to scrape the bottom and sides of the bowl with a silicone spatula.
While continuing to mix, add the butter in one tablespoon at a time, allowing each addition to fully incorporate before adding the next.
Knead the dough for a full 10 minutes on low speed, then turn the mixer up to medium speed and knead for another full 15 minutes.
Chill the dough (covered) in the refrigerator overnight, or for a minumum of 6 hours.
Knead the dough a few times to soften and warm it slightly, then roll it out to a large rectangle with a thickness of about 1/8-inch.
Spread the chocolate filling in an even layer all over the dough.
Starting at one of the shorter sides of the rectangle, roll the dough into a log shape.
Beginning near the top of the log, slice vertically through and then twist the two halves together, pinching back together at the base.
Transfer the unbaked loaf to a lightly greased, standard-sized loaf pan, cover loosely with a sheet of greased plastic wrap, and allow the bread to rise in a warm place for 4 to 5 hours.
Preheat the oven to 350 degrees F and sprinkle the bread with chocolate crumb topping.
Bake the bread for 35 to 45 minutes, or until deeply golden and crusty.
Cool completely in the pan before dusting with powdered sugar and slicing.
Place the chocolate, butter, and sugar in a medium bowl and melt together, either in the microwave (for about 1 to 1 1/2 minutes on full power), or over a double boiler, whisking until smooth.
Melt the butter in a small pot over low heat.
Add the flour, sugar, cocoa, and salt, tossing together with a fork until crumbly.
*Instant yeast may be substituted. Rise time may need to be reduced by 10 to 15 minutes. You'll know your dough is done rising when it has doubled in volume.
This recipe makes 1 loaf of chocolate babka.
Dough can also be mixed and kneaded by hand, or in a bread machine.