To make the dough:

1. Grease the short sides of a 9 x 5 loaf pan, and add a strip of parchment paper to completely over the bottom and long sides. Be sure to leave about 3-4 inches of overhang to make it easier to remove the baked loaf.
2. Combine the hot milk, yeast and 1 TB of the sugar in a glass measuring cup or small bowl and whisk well. Cover with a kitchen towel and allow to proof for 5 minutes.
3. While the yeast is proofing, combine the remaining 1/3 cup sugar, salt, cinnamon and 1 cup of the flour in a large mixing bowl. Whisk to evenly mix.
4. Once the yeast has proofed, it should be a few inches taller and very foamy. Add the yeast mixture, soft butter, egg yolks and vanilla extract to the sugar/flour/cinnamon mixture and use a spatula or wooden spoon to fold everything together for 30 seconds. Don’t be rough or use a lot of pressure.
5. Add a second cup of the flour and continue to mix for another 30 seconds. Again, don’t be rough. The dough will come together beautifully when you knead it. At this point, there should still be some visible streaks of butter.
6. Add 1/2 cup of the flour and mix until the dough has somewhat pulled together and looks pieced and shaggy.
7. Of the original 2 2/3 cups of flour you started with, there should be 2-3 tablespoons remaining. Dump that extra flour onto your countertop, and turn out the dough on top of it. Be sure to use the spatula or wooden spoon to scrape the bowl and get all of the dough pieces onto the countertop.
8. Knead the dough for 3 minutes. It should pick up all the dry pieces and excess flour, and become soft, smooth and elastic. Place the dough into a greased bowl, cover with a kitchen towel, and allow to rise in a warm, draft free area until doubled. Since this dough is richer and has more fat, allow up to 4 hours for the first rise. Mine was doubled in 3 1/2 hours.

To make the crumble topping:

1. After you begin the first rise, make the crumble topping so that it’s easy to grab later on. Combine the brown sugar, flour and cinnamon in a small bowl and stir together until evenly mixed. Add the cold butter and use your hands to work everything together until it has the consistency of wet sand. It’s okay if the butter softens a bit as you work with it, because you’ll be storing the crumble in the fridge before you use it.
2. Once the crumble is done, cover and refrigerate until needed.

Fill, Shape and Bake the loaf:

1. After the dough has doubled, punch it down to deflate it and use a rolling pin to create a 12 x 16 inch rectangle. You should not need any additional flour to roll out the dough. Spread the apple butter evenly over the dough, leaving at least an inch wide border around the edges.
2. Beginning with the longer side, gently roll the dough into a 16″ long log and tightly pinch the seam and ends closed. Create a “U” shape with the dough log, making sure the the “U” bend is curved AWAY from you. Make a figure 8 with the dough log, tucking the sealed ends underneath and forming a loaf. See visual aid in post.
3. Add the shaped loaf to the prepared loaf pan, and cover with a kitchen towel. Allow to rise in a warm, draft free place for another 90 minutes. 30 minutes before the dough is done rising, preheat the oven to 350 degrees.
4. After the second rise in the loaf pan, the dough should have crowned about an inch above the edges of the pan. Brush the loaf with the egg wash, and use a skewer or cake tester to poke about a dozen holes in the loaf. This prevents gaps from forming around the apple butter swirls.
5. Evenly sprinkle the loaf with the crumble topping and bake for an hour. After baking, remove the babka from the oven and allow to rest for 15 minutes before removing from the pan to a cooling rack.
6. Cool completely before slicing.