Wash the yuzu thoroughly, then separate the peel and flesh.
Mix the yuzu flesh with sugar to make yuzu syrup.
Put cake flour, sugar, and butter in a bowl and rub by hand until it forms coarse crumbs.
Spread the crumble dough evenly on an oven pan.
Bake in a preheated oven at 180°C for 15 minutes.
After cooling, top the crumble with yuzu syrup to finish.