Dough
¾ c milk, warmed to 80-90F
2 ¼ tsp (1 packet) active dry yeast
4 Tbsp unsalted butter
3 Tbsp sugar
2 egg yolks (reserve the whites, see below)
1 tsp pure vanilla extract
2 eggs (whole)
3 ½ - 4 c unbleached all-purpose flour
1 tsp salt

Filling
1 c brown sugar
1 Tbsp cinnamon
¼ tsp salt
2 Tbsp butter melted and cooled
1 egg white (see above)

Egg Wash
1 egg white (see above), lightly beaten

In a small bowl, mix the warmed milk and yeast. Set this mixture aside for 5-10 minutes, until the yeast begins to foam. While the yeast is starting, cream the butter and brown sugar together with an electric hand mixer in a medium bowl. Add the egg yolks, one at a time, beating between each addition. Add the eggs, one at a time, beating between each addition. Set this mixture aside. Give the yeast mixture a stir, then add it to the bowl of your bread machine (fitted with the dough paddles). Pour the egg and butter mixture over the milk. Add 3 cups of flour and the salt. Start your bread machine on its Dough Cycle. Watch your dough as it begins to knead. Once it looks like the ingredients are completely mixed, add more flour, a ¼ cup (or less) at a time, letting the machine knead between each addition, until the dough comes together and pulls away from the sides of the bowl. Once the dough is pulling away from the sides of the bowl, close your bread machine and let the machine run through its Dough Cycle. When the cycle is done, you are looking for the bread to be about double its bulk

Filling
While the dough is rising, make the filling by whisking all of the filling ingredients together in a medium bowl, until smooth. Set aside.

Putting It All Together
Grease a 9x5 loaf pan and line it with greased parchment paper. Tip the dough out of its rising bowl onto a well-floured surface. Punch the dough down and roll it out into a roughly 18x15 inch rectangle. Spread filling evenly over dough, leaving a 1 inch border on the long sides. Roll the dough, starting from one of the long sides. Cut the roll in half, lengthwise, turning it into two strands. Twist the two strands together, trying to keep the cut (exposed filling) side on top, as much as possible. Finally, shape your twisted dough into a figure 8, again keeping the cut sides up as much as possible. Place this twisted figure 8 into the greased and lined loaf pan. Cover the dough in the pan loosely with plastic wrap and let rise for 30 minutes. After 30 minutes, preheat your oven to 350F. When the dough has risen slightly and looks puffy, remove the plastic wrap and brush the top of the dough with the beaten egg white egg wash. Bake the bread at 350F for 45-55 minutes, until the top crust is deeply golden and the loaf sounds hollow when tapped. (The internal temperature of the loaf should read around 180F when the bread is done). (It may be helpful to place a piece of aluminum foil or an aluminum foil lined baking sheet on the rack under the bread to catch any filling that my bubble out of the loaf.) Once the loaf is done, cool the bread in the pan for 10 minutes, before gently removing the bread from the pan to continue to cool for 10-20 minutes before slicing. The babka will stay fresh stored in airtight container at room temperature for up to 3 days, then move the bread to the refrigerator.