In a small bowl, add the yeast to the warm water. Allow it to sit undisturbed until it begins to froth, about 5 minutes.

Meanwhile, grease two 8-inch round pans. Line the bottom of each pan with parchment paper. Set them aside until needed.

Heat the milk until quite warm to the touch. Pour the warm milk into a large mixing bowl or the bowl of your stand mixer. Cut the butter into smaller pieces and add to the warm milk, stirring until melted. Stir in the sugar, salt, egg yolks, and yeast mixture. Add the flour and stir until well combined.

Knead the dough until smooth and elastic, for about 5 minutes. This can be done by hand or with your stand mixer with the dough hook attached.

Grease a large bowl, add the dough and turn once to coat. Cover with a towel or plastic wrap.

Set aside in a warm place away from drafts to rise until doubled, for about two hours. Enriched doughs typically take a long time to rise.

Beat the softened cream cheese until light and fluffy. With the mixer running, pour in the sugar and salt, then the egg yolk and flour. Mix until well combined.

In a small mixing bowl, whisk together the flour and sugar. Cut in the butter until it is in pea-sized pieces. A pastry blender is a useful tool here, but you can also use your fingers to rub the butter into the flour mixture.

Do your best to divide the dough into two equal parts. On a lightly floured surface, place one part of the dough and roll it into a rectangle roughly the size of a half sheet (13" x 18").

Spread half of the filling mixture evenly on top, being sure to leave a one-inch border all around. Fold the edges over on all sides to help keep the filling in.

Then, begin to roll the dough, starting from the long edge furthest from you and moving towards you. If the dough isn't rolling freely, give it a nudge by guiding it underneath with a bench scraper or flat metal spatula.

Pinch the final seam to keep it together, and then twist the dough into a spiral, tuck the tail under and place in one of the prepared pans. Repeat with the remaining dough and filling.

Brush both loaves with the egg wash and sprinkle with the crumb topping.

Cover with plastic wrap and set aside in a warm place until the dough begins to rise above the rim of the pan, up to another hour. Midway through the second rise, preheat the oven to 350℉.

Bake the loaves for 45 minutes or until they register 190℉ in the center. You can also test for doneness by inserting a toothpick near the center. When done, the toothpick should come out clean.

Allow the babka to cool for 5 minutes in the pan then run a knife gently around to loosen the edges from the pan. Continue to let it cool completely before removing from the pan. Enjoy!