• In the bowl of a stand mixer fitted with the dough hook attachment or a large mixing bowl combine the sourdough starter, whole milk and granulated sugar. Stir until incorporated.
• Note: I would recommend doing this dough with a mixer if possible. It is a pretty sticky dough and requires a long knead.
• Then add the bread flour and mix for one minute on low speed until the dough is shaggy. At this point let the dough rest or autolyse for 20 minutes.
• After the 20 minute autolyse add the salt and eggs one at a time while the bread begins to knead on the lowest setting add the butter one tablespoon at a time. This helps the butter become well incorporated.
  
• Knead the bread for 15-20 minutes. This may seem like a long time, but it is necessary to build strong gluten strands. If it doesn’t seem to be passing the windowpane test you may want to knead it for longer.
  

What is the windowpane test?

• The windowpane test is used in bread making to know if you have kneaded your bread long enough. When making brioche this can be very helpful to know when it is done being kneaded.
• When you have been kneading the bread for quite a while take a little piece of dough in your hand and stretch it carefully. If you can see light through the dough without it ripping, then you have kneaded the bread successfully. However, if the dough rips, then the gluten formation is not fully developed, and you should knead for another 3-5 minutes, check again and repeat as kneaded…ha! I couldn’t help myself…needed.
• Once your bread has passed the windowpane test remove the dough, scraping the sides of the bowl, to a lightly greased bowl. Cover with plastic wrap and let rest on the counter for 1-2 hours. Then place in the fridge overnight or for 8-10 hours.
• The next day, remove the bread from the fridge and place on a clean work surface. You will now shape the loaf. You can do the shaping two different ways:

Braiding the loaf: (my favorite way)

• To shape the loaf this way, divide the dough into three equal pieces and form a log with each that is about 14 inches long. You can do this by rolling it with your hands on a clean work surface.
  
• After you have 3 - 14-inch logs you can join them together at the top. Placing the two side logs at the top under the middle one. From here, start braiding the loaf and once you reach the other side tuck the ends under the loaf and place in a greased high sided 9 in loaf pan.
  

Six Balls of Dough:

• The other method of shaping the loaf you could use is to divide the dough into 6 equal pieces. Roll them on the counter to get a uniform ball and place the dough balls 3 x 2 into the loaf pan.
• Once you have shaped your brioche loaf you will let it set in a warm spot, covered with a damp towel for 8-12 hours. (I usually place mine in the oven with the light on.) This is when you let the dough rise and the bulk fermentation.
• This step can take quite a while so don’t rush it. The best way to tell if your bread is ready to bake is if it has risen about an inch over the loaf pan. Remember sourdough brioche dough can take a while to rise.
  
• Once it has fully risen preheat your oven to 350 degrees. (Make sure to take the loaf out of the oven if you are letting it proof in there.)
• Bake your loaf in the preheated oven for 35-42 minutes until golden brown.
  
• You want to be sure that the loaf is cooked through so make sure to leave the loaf in until it is a golden brown but not burnt!
• When it comes out of the oven slather the top of the hot loaf with butter and remove to a cooling rack to cool.
  
• Let your loaf completely cool before slicing it and enjoy!