1.Add the milk, yeast and honey into the insert of a standing mixer and mix gently to combine. Set aside for 10 minutes to allow the yeast to activate.
2.Add 5 eggs and yolk, and mix gently to break the egg yolks. Add the vanilla, sugar, flour and salt, and mix to form a scraggly dough.
3.With the dough hook attachment, knead the dough on speed 3 for 5 minutes. Divide butter into 4 portions. Add the first portion of butter, in increments, after the first 5 minutes of kneading. Allow the butter to be mixed well into the dough for 2 minutes. Repeat with the other 3 portions of butter, kneading the dough for about 2 minutes after each addition. Make sure to stop the mixer to scrape down the bowl.
4.Once all the butter is incorporated, scrape the bowl and knead the dough on speed 6 for 15 minutes. The dough will have been kneaded enough when it can be lifted cleanly off the bottom of the bowl when picked up with the dough hook. It will be very soft and tacky to the touch, but shouldn’t stick to your fingertips.
5.Flour your work surface, and turn the dough out onto the floured surface. Lightly flour your hands and the surface of the dough. Fold in the edges of the dough towards the middle and gently press them into the dough. Carefully flip the dough over, and then with the heel of your palms, shape the dough to form a tight ball. Carefully pick up the dough ball and place it back in the mixer bowl. Let it rise until it has doubled in size, in a warm place for about 1 hour.
6.Turn the dough out onto a lightly floured surface, and press down gently to deflate the dough with your hands. Fold in the edges again as before towards the middle and press them in. Carefully flip the dough over (seam side down now). Tighten the dough into a ball with a smooth, taut surface (using the edges of your palms). Transfer the dough into the mixer bowl again. Cover and let it chill in the fridge for at least 8 hours, or up to 24 hours.
7.Remove the chilled dough from the fridge. Spray two standard loaf pans with cooking spray. Turn the dough out onto a lightly floured surface. Deflate the dough by flattening it lightly. Measure the weight of the dough, and then divide it into two EQUAL portions.
8.Divide one portion of the dough into 3 equal portions. Flatten each portion into a small rectangle. Then tightly roll up the rectangle to form a tube. Using your palms, and a back and forth motion, roll out the dough into a 14 inch long bread rope. Repeat with the other two portions. Bring the ends of the three ropes together and pinch to seal. Braid the dough, while being careful to avoid any loose folds and to not stretch the dough ropes at the same time.
9.Pinch to seal the other end. Using your palms, press down the ends of the bread to flatten them against the work surface. Tuck the flattened ends to get a, rounded loaf. Carefully transfer this to the loaf pans. Flatten slightly to fit the loaf pan. Cover with plastic wrap and let sit for 2 hours or doubled.
10.Preheat oven to 325 degrees. Scramble 1 egg in a small bowl and brush the tops of each loaf with egg wash. Bake until golden brown about 35-45 minutes. Remove from oven and let cool slightly, about 5 minutes. Flip the bread out of the pan and onto a cooling rack. Cool completely and store in air-tight container.