Let's introduce the elephant in the room….death by butter! Making Brioche takes time might as well make a day of it.
Add Milk, Yeast, Egg and HALF the flour. Mix in a bowl.
Make a flour blanket and add the remaining half of the flour on top, no not mix in. Cover at let sit at room temperature for minimum 45 min and up to three hours.
Add remaining ingredients EXCEPT the butter on top of the sponge. Mix well by hand or use your processor for about 15 min.
Add Make sure the butter is firm and not melting. Note: If you use melted butter you're going to lose volume and you'll be disappointed with the results. So get it right, eh!
Blend the butter into the dough till it's mixed then turn it off.
Add dough to a lightly oiled bowl and cover till double in size at room temperature. One to two hours.
Gentle deflate the dough with some hand twists. Cover and put in fridge for one hour.
Put a very light dusting of flour on counter and place dough on it. Do a couple of business letter turns and brush off any flour.
Loosely wrap the dough and keep in fridge for 6 hours to 2 days in a zip lock bag.