Dough. If using active dry yeast, pour water (should be generally between 105°F and 110°F) into mixing bowl of electric mixer. Sprinkle with yeast and about 1 teaspoon of the sugar. Stir gently to hydrate the yeast. Let it sit for 5-10 minutes to get foamy. If using instant yeast, add it, together with the warm water, to the rest of the ingredients in step 2.
Add the flour, rest of the sugar, yolks, oil, and honey. With the dough hook attachment, knead the mixture for about 3-5 minutes.
With the mixer on low, slowly add the salt. Knead for an additional 2-3 minutes until the salt is fully absorbed and the dough passes the windowpane test.
Place dough in ungreased bowl, cover with plastic wrap, and let rise in warm area for about 3 hours. (Alternatively, allow the dough to rise for 1½ hours, then place it in the refrigerator overnight. In the morning, remove it from the refrigerator and continue immediately with Step 6.
Prepare filling. While dough is rising, in a small mixing bowl, mix together the light brown sugar, cinnamon and flour. Set aside
Shape dough. Gently deflate the dough by pulling a piece from the bottom and folding it over itself, turning the bowl so you can do four similar folds.
Spray two 8½ inch by 4½ inch loaf pans. (Or just place parchment in them.)
Beat the egg and set aside. Divide dough in half, preferably by weight. Cover one half with plastic wrap while working with the other half. Roll the dough out to a rectangle, approximately 18 inches by 10 inches. If the dough retracts too much, cover it with plastic wrap and let it rest 5-10 minutes. Using a pastry brush, apply a liberal coating of the beaten egg , leaving approximately ½ inch untouched along one of the 10 inch long sides. Sprinkle the dough with half of the filling. Use a rolling pin or the palms of your hands to press the filling into the dough. Starting from the side where there Is filing along the bottom of the dough, tightly roll the dough into a log so that you have a log approximately 10 inches long. Press the ends of the top where there was no egg wash into the log. Slice the log down the middle in half, exposing the layers of filling. Form an X with the two pieces, and cross the two over each other starting from the middle going down towards you. Repeat from the middle going up. Place dough in prepared pan. Cover loosely with plastic wrap and allow to sit until doubled in size, approximately 1½ hours. Repeat with second mound of dough. Cover the remaining egg wash and refrigerate for the crumb topping.
Prepare crumb topping. In a small bowl, use a fork to mix together all the crumb ingredients. They will form into crumbs. Cover and store in refrigerator.
Preheat oven to 350° F. at the 1 hour mark.
Sprinkle Crumb Topping. Just before you are ready to bake, remove the crumbs from the refrigerator. With a pastry brush, brush the remaining egg wash all over the top of the loaves, including where the filling is exposed. Sprinkle the crumbs on top and on the sides. Gently press them in. Line the rack under the rack on which you will bake the babkas with a large baking sheet or a large sheet of aluminum foil to catch any crumbs that fall off the tops of the babkas while they bake.
Bake 50-70 minutes, until the inside temperature reaches 205° F.
Allow to cool in pan for 5 minutes. Use a metal spatula to release the babkas from the sides. Turn pans over to release the babkas. Some of the crumb topping will fall off, so just accept that. (It give you something to munch on while the babkas cool!) If the babkas are stuck in the pans, hold the bottom of the pan over a medium flame on your stovetop for just a few seconds. The heat should help you release the babkas from the pan. Allow to cool completely on wire rack.