Wash the rhubarb, peel and cut into pieces of about 1 cm (if the rhubarb is very thick, a little shorter).
Roast the breadcrumbs in butter and then mix with cinnamon and cardamom.
Mix rum, honey and roasted breadcrumbs with the rhubarb.
Spread the puff pastry on a baking tray covered with baking paper and spread the filling mixture evenly on it. Roll up tightly and brush with a little milk.
Bake the strudel in a hot oven according to the package instructions.