(makes 1 medium or 2 small loaves)   

Firm Starter

100g AP flour
50g (approx) water
50g ripe storage starter (mine is at 100% hydration)

Mix the flour and starter, adding just enough water to make a firm white dough ball.

Proof for 5 hours at room temperature or until well over doubled in volume.

Final Mix

200g all purpose flour 
200g bread flour
80g sugar
7g salt (more if using unsalted butter)
200g firm white starter
100g (approx) milk 
150g butter (soft enough to easily mix)
3 large eggs + 1 egg yolk
1/2 tsp lemon extract + grated zest of 1 lemon (optional) 

Beat the eggs, sugar, lemon zest, lemon extract, salt and bread flour together into a smooth paste. Set aside for at least half an hour.

Mix the all purpose flour and milk, using just enough milk to make a smooth stiff dough. Set aside for 15 to 20 minutes.

Knead the starter and flour/milk dough together well. Set aside for 15 to 20 minutes.

Fold the egg mixture into the dough, a little at a time.  This will get very messy but stick with it.  It will come together eventually.  

Using frissage (http://www.thefreshloaf.com/node/2882/eye-opening-techniques)  incorporate the butter into the dough, a little at a time.

You will end up with a very slack, shiny dough which barely holds together.

Apply a few french folds (http://home.att.net/~carlsfriends/jimpics/index.html) to increase strength in the dough.  Allow the dough to rest for an hour in a bowl. 

After resting, turn out the dough onto a well floured surface.

Divide and shape as desired (traditional brioche à tête may not be possible with such a slack dough).

Place into appropriate baking tins and cover loosely.

Proof until doubled in bulk (up to 8 hours!)

Preheat the oven to 400F

Very carefully brush the tops with beaten egg and score lengthwise with a serrated blade.

Bake the brioche for 30 minutes (or until a poked skewer comes out clean). If the top crust gets too brown then cover with foil for the remainder of the baking time.

Allow to cool for at least half an hour.  Enjoy!

--FP