(3 loaves)1½ cups warm milk
2 packages dry yeast
1¾ cups plus a pinch of sugar
3 whole large eggs
2 large egg yolks
6 cups flour
1 tsp salt
1¾ cups (3½ sticks) unsalted butter
2¼ pounds semisweet chocolate, very finely chopped
2½ tbsp ground cinnamon
1 tbsp heavy cream
Streusel topping:
1⅔ cups confectioners' sugar
1⅓ cups flour
12 tbsp unsalted butter
Pour warm milk into a small bowl. Sprinkle yeast and a pinch of sugar over milk. Let stand until foamy, about 5 minutes. Whisk together ¾ cup sugar, 2 eggs and egg yolks. Add egg mixture to yeast mixture, and whisk to combine.
In the bowl of an electric mixer combine flour and salt. Add egg mixture and beat on low speed until almost all the flour is incorporated. Add 2 sticks of butter and beat until flour mixture and butter are completely incorporated, and a smooth soft dough that's slightly sticky when squeezed is formed, about 10 minutes.
Turn dough out onto a lightly floured surface, and knead a few turns until smooth. Butter a large bowl, place dough in bowl and cover tightly with plastic wrap. Set aside in a warm place to rise until doubled in bulk, about 1 hour.
Place chocolate, remaining cup sugar and cinnamon in a bowl and stir to combine. Using two knives or a pastry cutter, but in remaining butter until well combined. Set aside.
For the streusel topping: In a large bowl combine sugar, flour and butter. Using a fork, stir until fully combined with clumps ranging in size from crumbs to 1 inch.
Generously butter three 9-by-5-by-2¾-inch loaf pans and line them with parchment paper. Beat remaining egg with cream and set aside. Punch back the dough, and transfer to a clean surfave. Let rest 5 minutes. Cut into 3 equal pieces. Keep 2 pieces covered with plastic wrap while working with the remaining piece. Roll dough out into a 16-inch square. It should be ⅛ inch thick. Brush edges with egg wash. Crumble ⅓ of the chocolate filling evenly over dough, leaving a ¼-inch border. Roll dough up tightly like a jelly roll. Pinch ends together to seal. Twist 5 or 6 turns. Brush top of woll with egg wash. Carefully crumble 2 tbsp filling over the left half of the roll, being careful not to let mixture slide off. Fold right half of the roll over onto the coated left half. Fold ends under, and pinch to seal. Twist roll 2 turns and fit into prepared pan. Repeat with the remaining 2 pieces of dough and remaining filling.
Heat oven to 350 degrees (Fahrenheit). Brush the top of each loaf with egg wash. Crumble ⅓ or streusel topping over each loaf. Loosely cover each pan with plastic wrap, and let stand in a warm place 20 to 30 minutes.
Bake loaves until golden, about 55 minutes. Lower oven temperature til 325 degrees and bake until babkas are deep golden, 15 to 20 minutes more. Remove from oven and transfer to wire racks until cool. Babkas freeze well for up to 1 month.
