For the 1st step
Place the milk, the flour and the yeast in the bowl, mix it well. Set aside for 12 hours at room temperature.
For the 2nd step, 12 hours later
In the bowl where there is your preparation, add the egg yolks, the vanilla, the butter and the sugar, mix well.
Add the yeast and gradually add the flour. It should start to form a dough, a little sticky at first.
Knead the dough for 10-16 minutes.
Take the dough, separate it in 2 equal balls.
From each ball, divide it in 3 parts and make rolls to braid them.
Once you have braided both your dough, let them rest for 1h30minutes.
For the egg wash:
Take the egg yolk and the milk and stir well.
With a brush, apply some on each braid.
Place in the oven at 360F for 20 minutes or until your brioches are golden.