1) Knead flour with a pinch of salt, 1 tablespoon of oil and 1.25 dl of warm water; formed a stick, wrap it in cling film and let it rest in the fridge for 2 hours.
2) Peel the onions, cut into 1/2 cm thick slices and cook for 20 minutes in a covered pan over low heat with 30 g of butter, brown sugar, bay leaf, and red vinegar. Raise the lid, add 80 g of shelled currants, cook over high heat for about 5-6 minutes, hold aside 2 tablespoons of onions to decorate and let cool.
3) Toast in the pan the breadcrumbs with the remaining butter e let it cool. Roll out the strudel dough in a very thin rectangular sheet; sprinkle it with the toasted breadcrumbs leaving a margin of 3 fingers free, distribute yourselves over half of the onions, the ham, the cheese cut into slices and complete with the remaining onions. Fold back one long side of the dough inwards and roll it over the filling.
4) Transfer the strudel in a baking tray lined with parchment paper, brush it with the yolk diluted with a few drops of water, transfer it to the oven and cook at 200 ° for 45 minutes. Take it out of the oven, slice it and serve it with the onions kept aside, the remaining blackcurrant cicchi and the Castelfranco radicchio, chopped and seasoned with oil, salt and pepper.
