Very soft brioche loaf

An exceptionally soft, fairly neutral loaf, not too sweet, for sweet or savoury use. I loved it with breakfast jam. This recipe comes from 55 Winston 55 , a perfect recipe if you respect rising times. STARTER
30 G ITALIAN 00 FLOUR
180 ML WATER
BRIOCHE
250 G ITALIAN 00 FLOUR
200 G MANITOBA FLOUR
200 ML MILK
40 G BUTTER
40 G SUGAR
3.5 G DRIED YEAST
1 TEASPOON FINE SALT

TO BRUSH
1 EGG YOLK
MILK EQUAL TO YOLK WEIGHTI mix 30 g flour with 180 ml water in a small pan.I heat and stir without lumps for 5 minutes until thick, smooth and sticky.I put in a small bowl, cover and refrigerate for 6 hours. I put both flours and yeast in the mixer. I add sugar.I add prepared starter.I fit hook and knead.I gradually add milk and knead for 10 minutes.I add a teaspoon salt. Then soft butter cubes gradually.I knead for 10 minutes, put in a lightly floured bowl, cover with cling film and rise in switched-off oven with light on for 2 hours.It should double.I turn onto work surface.I divide into 3 equal pieces.I flatten dough. I roll it up.I roll into a parcel.I make all three. I line a 30 X 10 loaf tin with parchment and add dough. I cover and rise another 1 hour. It should double.I weigh yolk, add equal milk weight and beat with a fork.I brush dough. I bake at 180°C conventional for about 30/40 minutes, checking and covering with foil if too dark.I cool slightly, unmould and cool on a rack.