3: Stop kneading to add 10 g vanilla sugar, 50 g caster sugar and 50 g butter. Knead again, still on slow speed, until the butter and sugar are completely mixed un.
4: Gather the dough (it is quite normal for this to be very sticky) into a ball and transfer to a clean bowl. Cover with a sheet of plastic. Leave to rest for 1 hour.
5: After resting, "break" the dough (similar to knocking back with a firmer dough) by stretching it upwards and letting it fall back sharply into the bowl. Do this 2 or 3 times.
6: Gather the dough into a ball again, cover with plastic film and leave in the fridge for at least 4 hours or overnight.
7: The dough will be easier to handle when it is really cold. Tip it onto a floured work surface and press it flat, then shape into a loaf: round, long (like this one), or whatever you prefer. Place the loaf on a baking sheet.