Whisk the warm milk, yeast, and 1 Tablespoon of sugar together in the bowl of your stand mixer fitted with a dough hook or paddle attachment. Cover and allow to sit for 5 minutes. *If you don’t have a stand mixer, use a handheld mixer or mix the dough by hand using a silicone spatula or wooden spoon.*

Add the remaining sugar, the butter, egg yolks, salt, and 1 cup (125g) flour. Beat on low speed for 30 seconds, scrape down the sides of the bowl with a silicone spatula, then add another 1 cup of flour. Beat on medium speed until relatively incorporated (there may still be chunks of butter). Scrape down the sides of the bowl with a silicone spatula. Add 1/2 cup of flour and beat on medium speed until the dough begins to come together. As the mixer runs, add another 2–4 Tablespoons of flour depending on how wet the dough looks. (I usually add another 2 Tbsp, which makes it about 2 and 2/3 cups of flour total.) This should be a very soft and almost creamy-feeling dough. Do not add more flour than you need.

Keep the dough in the mixer (and switch to the dough hook if using the paddle) and beat for an additional 6-8 full minutes, or knead by hand on a lightly floured surface for 6-8 full minutes. (If you’re new to bread-baking, my How to Knead Dough video tutorial can help here.) If the dough becomes too sticky during the kneading process, sprinkle 1 teaspoon of flour at a time on the dough or on the work surface/in the bowl to make a soft, slightly tacky dough. Do not add more flour than you need because you do not want a dry dough. After kneading, the dough should still feel a little soft. Poke it with your finger—if it slowly bounces back, your dough is ready to rise.

Lightly grease a large bowl with nonstick spray. Place the dough in the bowl, turning it to coat all sides. Cover the bowl with aluminum foil, plastic wrap, or a clean kitchen towel. Allow the dough to rise in a relatively warm environment for 3–4 hours or until nearly double in size. This dough is rich with fat, so it takes longer than other doughs to rise. (If desired, use my warm oven trick for rising. See my answer to Where Should Dough Rise? in my Baking with Yeast Guide.)

Melt 1 Tablespoon of butter in a large skillet on the stove over medium heat. Add the apples. Stir and cook until the apples are slightly softened, about 3 minutes. Remove from heat and stir in lemon juice to help prevent browning. Set aside. For the rest of the filling in this step, make sure you don’t prepare it too far in advance because the butter will solidify and spreading onto the dough will be difficult. Melt remaining 2 Tablespoons of butter in a medium heatproof bowl in the microwave (or use the stove). Stir in brown sugar, flour, cinnamon, salt, and vanilla extract until crumbly and combined. Stir in the egg white. Set aside.

Grease a 9×5-inch loaf pan.

When the dough is ready, punch it down to release the air. Flour a work surface, your hands, and a rolling pin. Roll the dough out into a 12×16-inch rectangle. Carefully and slowly spread the cinnamon filling mixture on top. (The dough is quite soft underneath and you don’t want to tear it.) Add the apples in a single layer. Using floured hands, tightly roll up the dough to form a 16-inch long log. If any parts of the dough feel soft as you roll it up, add a sprinkle of flour as I do in the video above. Place the log on its seam. Fold in half, then twist it to form a figure 8. Pinch the ends together. Use the video tutorial and photos above as a visual. Place in prepared loaf pan.

Cover shaped babka with aluminum foil, plastic wrap, or a clean kitchen towel. Allow to rise until it’s puffy and nearly reaches the top of the loaf pan, about 1–1.5 hours.

Mix the brown sugar, flour, and cinnamon together. Add the cold butter and using a pastry cutter or a fork, cut butter into the brown sugar mixture until pea-size crumbles form. Refrigerate until ready to use.

Preheat oven to 350°F (177°C). Place a baking sheet on a lower oven rack to catch any juices or crumbles that may drip/drop down. (Has only happened to me once!)

Carefully brush the surface of the babka with last remaining egg white. Using a toothpick, poke 10–12 holes all over the top of the loaf. This allows steam to escape from inside the loaf so the layers don’t separate. Sprinkle with crumble topping.

Bake for 60–65 minutes or until golden brown on top. If you gently tap on the loaf, it should sound hollow. If you notice the top browning too quickly, loosely tent the pan with aluminum foil. (I usually add aluminum foil over the loaf around the 25-minute mark.) Remove from the oven and allow bread to cool in the pan for at least 30 minutes before slicing and serving. For neat slices as pictured above, I recommend cooling completely before slicing. A serrated knife is best for slicing.

Cover leftover babka tightly and store at room temperature for 2 days or in the refrigerator for up to 1 week.