Set aside 2/5 cup (100 g) crushed walnuts for sprinkling at the end. Mash together the other walnuts and the biscuits.
Sprinkle this biscuit/walnut mixture over the sheets. Wrap into a roll, cut into pieces and arrange them upright in the tray.
Pour the melted butter and oil over them.
Bake at 356°F (180 °C) until golden. Once cooled, pour the hot syrup over it and sprinkle with the remaining walnuts.