To make poached persimmons, place sugar in a saucepan, cover with 500ml water and bring to a simmer over medium heat, stirring to dissolve sugar. Add persimmon wedges and place a small plate on top of them to keep submerged in poaching liquid, adding a little extra water to cover if necessary, and cook for 5 minutes or until softened. Remove pan from heat and allow to cool in liquid.
Meanwhile, combine sugar and rosewater to make a paste. Stir through walnuts. Set aside.
Place whole persimmons in a food processor and process to a smooth purée. Place 500 ml purée in a large bowl. Add 600g flour, mixing until combined. Gradually add enough of the remaining 75g flour until dough can hold its shape – it should still be quite sticky. Using floured hands, knead dough in bowl until smooth. Cover with plastic wrap and leave to rest for 30 minutes.
Turn dough out onto a heavily floured work surface and divide into 10. Shape one piece into a ball, pressing down with palm to flatten slightly, then roll out to a disc approximately 11 cm in diameter. Using your fingertips create a thinner 1 cm border around the edge. Place some of the reserved walnut filling into the centre of the disc, then draw up edges to enclose filling, pinching to seal. Gently flatten with the palm of your hand. Repeat with remaining dough and walnut filling.
Fill a large frying pan 1 cm-deep with oil and heat over low heat. Working in 2 batches, cook cakes, covered and turning halfway, for 20 minutes or until filling has melted and dough is golden and cooked through. Drain on paper towel. Place cakes on plate and serve warm with poached persimmon and dried osmanthus flowers.
