For the Dough:
- 1 cup whole milk, warmed to 115°
- 2¼ teaspoons active dry yeast
- ¼ cup, plus 1 teaspoon, granulated sugar, divided
- 5¼ cups flour, plus more for dusting
- 1 teaspoon kosher salt
- ½ teaspoon ground cinnamon
- ¼ cup light brown sugar
- 4 eggs, divided
- 1 stick unsalted butter, cubed and softened, plus more for greasing
For the Filling:
1. Make the dough: In a large bowl, combine the milk, yeast and 1 teaspoon of the granulated sugar. Let it sit until it begins to foam, about 10 minutes. Meanwhile, in a medium bowl, whisk the flour, salt and cinnamon, and set aside.
2. To the foamy yeast mixture, add the remaining granulated sugar, the brown sugar and 3 eggs, and whisk to combine. Slowly stir in the flour until a dough forms, then transfer to a lightly floured surface. Using your hands, knead in the softened butter, a little at a time, until a smooth dough forms. Place in a greased bowl and cover with plastic wrap. Let rise in a warm place until doubled in size, about 1 hour.
3. Meanwhile, make the filling: In a medium bowl, stir the filling ingredients together until incorporated.
4. Assemble the babkas: Preheat the oven to 350° and grease two 9-by-5-inch loaf pans. Divide the dough into 2 balls. On a lightly floured surface, roll 1 ball of dough out into a 14-inch square, about ⅛inch thick.
5. Spread half of the filling evenly over the surface of the dough, leaving a 1-inch margin at the top of the square. Starting with the edge closest to you, roll the dough up tightly. Leaving ½inch of dough connected, cut the roll lengthwise in two. Twist the strands together and pinch at the end to seal. Carefully place the babka in one of the prepared pans.
6. Repeat this process with the remaining dough and filling. Cover both babkas loosely with plastic wrap and place in a warm area until the dough expands to fill the pan, 45 minutes more.
7. In a small bowl, beat the remaining egg and liberally brush onto each babka. Bake, rotating halfway through, until golden and cooked through, 40 to 45 minutes.
8. Let cool slightly, then remove each bread from the pan and let cool before slicing and serving.