In a small bowl, combine lukewarm milk, yeast and ¼ c of sugar. Set aside to bloom.
In the bowl of a stand mixer, combine remaining ½ c sugar and eggs. Using the paddle or whisk attachment, on medium speed, whip together. Add in the salt and stir. Next, add in the bloomed yeast mixture and stir. Add in both of the flours. Switch to a dough hook attachment and turn to mixer speed medium to incorporate the flours. Once they are incorporated, turn up the mixer speed to high. Let the dough knead for 8-10 minutes.The dough will be wet and sticky at this point but it should pull away from the edges when mixing.
Leave the dough in the mixing bowl and cover with plastic wrap. Place into the fridge for an hour or until doubled in size. Punch the dough down, remove and place into a larger, well greased bowl. Cover with plastic wrap and place back into the fridge overnight.
Make the Chocolate Ganache Filling
After the dough has set overnight and is doubled in size, remove from the fridge and let it set on the counter for 10 minutes. While the dough is setting, make the chocolate filling. In a small, microwave safe bowl, heat heavy cream for 1 minute. Pour over chocolate chips and let set for 1 minute. Stir the melted chocolate chips into the heavy cream. I find that using an emulsion blender works really well resulting in a very smooth ganache. Stir in the melted butter then set aside.
After 10 minutes has passed, turn the dough out onto a floured surface. Prep a 9x5 loaf pan by spraying it with baking spray and set aside. Cut the dough in half and set one half back in the bowl and back into the fridge until you are ready to use it later.
Roll your dough out to 18” long and 12” wide. This dough should be significantly longer than it is wide because it will help create the pretty folds in the babka. Using a rubber spatula or the back of a spoon, spread half of the chocolate ganache over the entire surface of the dough. Zest one orange over the surface. Roll the dough into a log. At this point, I like to cut a one inch piece from each end to square them up. Using a very sharp knife, cut down the center of the dough longways. I like to gently run the knife down the center, dip my knife in flour and continue to run through the dough. Pushing the knife down through the dough can cause the layers to press into each other. Have patience and reflour your knife as many times as you need to to prevent the dough and filling from sticking to your knife.
Once your dough is cut into two long pieces it is time to braid it. Pick up one side and place it over top of the second side. Pull the second side under the first overlapping piece and pull it over the first piece. Repeat until you have run out of dough. You should be able to braid it at least 3 times and ideally 5 times. Pinch the ends together so that they don’t open up when the dough is rising. Place into the prepared loaf pan and let rise until doubled in size. Repeat steps 6 and 7 with the other half of the dough.
Bake the Bread
Preheat the oven to 350 F. Once your dough has doubled in size, place into the preheated oven for 45-60 minutes. Your bake time will vary from oven to oven as well as how much your bread rose before baking. I like to tent a piece of tinfoil over the pan before I begin baking and removing it after it’s done baking to let it brown for an additional 3 minutes. Baking it with tinfoil on just helps to keep the top from browning too quickly and drying out. Again, browning time will vary from oven to oven.
Once your babka is baked, remove from the oven and let cool for 10 minutes to prevent burns from the hot filling. Serve and enjoy!
Storage: Babka may be stored in an airtight container or in a baggie for up to 3 days.