1: After preparing 500 g brioche dough, refridgerate for 1 or 2 hours or overnight, so that the dough becomes firm. Then roll out dough (sprinkle generously with flour) into a large rectangle about 1 cm or 0.5 inch thick.
2: Put this rectangle on a bigger sheet of cooking parchment. If necessary, reshape your rectangle after this transfer operation.
4: Now your goal is to roll up the dough to form a cylinder. It looks difficult, but in fact it's quite easy, thanks to the paper sheet. Use it to start rolling, without touching the dough, and so form the roll.
5: Continue until completely rolled up.
6: Put roll on a baking sheet, and refrigerate for about 2 hours, until the roll becomes quite firm.
7: After this time, remove roll from the fridge and with a large sharp knife, trimm off the ends to neaten. Note: you can cook these bits later.
8: Then cut the roll into slices about 3 cm or 1.5 inches thick, and arrange them in a round mould or tray, touching one touching another. That's why firm dough is absolutely essential, otherwise the slices will squash during cutting.
9: Cover mould with a plastic sheet, and leave in a warm place for 2 hours.
10: After this time, preheat oven to 180°C or 356°F. Glaze top of cake.
11: Put in the oven for about 30 minutes.
12: Turn out on a wire rack. When cake is cool, you can decorate it with 100 g fondant icing, melted in bain-marie or microwave oven.
Remarks
You can also put on the custard before rolling up: raisins, small pieces of dried apricot, chocolates chips, etc.