Combine dry yeast and warm milk. Leave to rest for 10 minutes at room temperature.
Put flour + egg + sugar + salt in a bowl. Add milk+ dry yeast. Knead for 3 minutes.
Add softened butter gradually while kneading. Knead for 7 minutes.
Form a ball and cover with a cloth. Leave to sweel for 1h30 at room temperature.
Degas the dough and cut into 4 doughs. Fold each dough 3 to 4 times and make balls. Cover with a cloth for 30 minutes at room temperature.
Spread the doughs to make 10 inches circles. Spread some Nutella on top of 1 dough leaving a 1/2 inch (1cm) border.
Put a second dough on top and spread Nutella again. Repeat with the third dough and cover with the fourth dough.
Cover with a 10 inches pan or plate and cut the exceedent dough. Put a glass on top of the dough, in the center.
Cut into 4, then 8, then 16 equal parts.
You have to create 8 branches. Each branch will have to parts. You'll have to twist the right part : from left to right and the left part : from right to left.
Press the borders of the branches. Remove the glass and cover with a cloth for 1h30 at room temperature.
Preheat the oven to 350°F (180°C). Combine the eg yolk with the milk and baste the top of the brioche.
