Step by step recipe:

1. 5 min.
   Put into a food-mixer bowl: ng0, 170 g egg, 40 g caster sugar, 5 g fine (or table) salt, 100 g butter, 8 g yeast and 50 g Soured dough (if possible).
2. 15 min.
   Knead for 15 minutes.
3. 1 hour
   Gather the dough more-or-less into a ball and cover the bowl with plastic film. Leave to rest for 1 hour at room temperature.
4. Meanwhile, shape the 120 g butter between sheets of plastic into a square about 4x4 inches (10 x 10 cm).
   
   This is the same idea as for croissants (though with less butter). You can see how to do it in this video.
5. 5 min.
   Once the butter is in the right shape, put it in the fridge.
6. 3 min.
   After the dough has rested for about an hour, "break" it: lift it and let it fall back heavily into the bowl (like knocking back a firmer dough, this releases the gas).
7. 12 hours
   Gather the dough into a ball once more, cover the bowl with the plastic film again and refrigerate overnight.
8. 3 min.
   Next day, mix 110 g granulated sugar and 10 g Vanilla sugar with a whisk, then set aside.
9. 5 min.
   Roll out the brioche dough into a large rectangle. This needs to be the same width as the square of butter and twice as long.
10. 1 min.
    Place the butter in the centre of the dough and remove the plastic.
11. 4 min.
    Fold the dough over the butter to envelope it completely.
12. 5 min.
    Turn the dough through 90° (1/4 turn) and roll out.
    
    Sprinkle half the mixed sugars over the dough and press in lightly with the rolling pin so that the sugar sticks to the dough somewhat.
13. 5 min.
    Fold the ends of the dough into the centre over the sugar, then fold in half again.
    
    Give another 1/4 turn and roll out. Repeat the operation with the remaining sugar.
14. Watch this video from the croissants recipe to see how to fold the dough.
15. 3 min.
    Give the dough a final 1/4 turn and roll out into a long rectangle.
16. 5 min.
    Roll the dough up from a long edge to make long roll.
17. 3 min.
    Use a brush and egg glaze to seal along the "seam".
18. 5 min.
    Cur the roll into slices about 1/2 inch (1 cm) thick.
19. 5 min.
    Arrange the slices in a spring-form tin or mould, but not too tightly, as they will swell during resting and cooking.
20. 1 hour
    Brush the tops, and the sides if possible, with beaten egg glaze.
    
    Leave in a warm place to rest for 1 hour.
21. 3 min.
    Preheat the oven to 390°F (200°C).
    
    Glaze the top a second time.
22. 40 min.
    Bake for 30 to 40 minutes.
    
    This must be turned out hot, before the caramel sets in the bottom of the tin.
    
    Your brioche is ready.