For the bread:
For the filling:
For the topping (optional):
1Start by making the filling. In the top of a double boiler, or in the microwave, melt the chocolate. Stir in the olive oil and cinnamon. Set the mixture to the side for now.
2Make the dough. Grease two 9x5-inch loaf pans with olive oil and set to the side. In a large bowl, combine the water and yeast. Once the yeast begins to bubble lightly, add the sugar, milk, egg, olive oil, and salt. Stir to combine.
3Using a dough scraper, add in the flour, starting with 2 cups and then working in the rest until the dough comes together into a slightly sticky but handleable mixture. Knead the dough for 2-3 minutes by hand; the dough will become smoother and slightly elastic.
4Form the dough into a ball and put in a lightly oiled bowl. Cover with a kitchen towel, and let the dough rest at room temperature for 1 hour, or until it has doubled in size.
5Gently deflate the dough using a fist (a gentle fist--not a knockout punch).
6Turn the dough out onto a floured work area and roll into a rectangle about 12 x 15 inches. The chocolate filling should have thickened by this point, to the thickness of peanut butter: easily spreadable, and not drippy. Spread the chocolate filling over the dough, covering it evenly, but leaving a small perimeter of dough uncovered on all sides.
7Cut the dough in half horizontally. Take the edge of each piece and roll it toward you, jelly-roll style. Now you’ll have two tubes of dough and chocolate.
8Place the tubes side by side, and press the ends together. Now, give the entire unit a twist or two, so that they look somewhat braided. The dough will become longer during this process.
9Cut the long loaf in half, and put half in each pan. Make sure that the dough is long enough to fill about ⅔ of the pan.
10Let the dough rest, covered with a kitchen towels, in the loaf pans for 1 hour or until it has filled out the pans.
11Near the end of this rising period, preheat the oven to 350 degrees F.
12Prepare the topping while the oven preheats. Combine all of the ingredients in a small bowl, stirring until they come together into a crumbly streusel mixture. Brush the tops of the loaves lightly with olive oil, then sprinkle with the topping.
13Bake for 30 minutes or until deep golden brown. Remove from the oven and let cool in the pans before serving.
14Store well-covered babka at room temperature for up to 3 days, or store in the freezer for up to month.