Drain the sauerkraut. Peel onion and cut into fine strips. Heat the oil in a pot and fry the onion in it. Add sauerkraut with bay leaf and juniper. Season with salt and pepper and braise covered for about 10 minutes.
Leave to cool and remove the bay leaf and juniper. Remove the skin from the blood sausages. Lay the filo pastry sheets on top of each other. Cover about 1/3 of the surface with sauerkraut. Place the blood sausages on top and roll up the dough sheets into a strudel.
Melt the fat. Place the strudel on a baking tray lined with baking paper, brush with the fat and bake in a preheated oven (electric range: 200 °C/ gas: level 3) for approx. 30 minutes. In the meantime, peel and quarter the apple and cut out the core.
Cut the apple into small cubes. Caramelise the sugar in a saucepan until light and deglaze with wine. Let simmer for about 5 minutes. Clean, core and wash the chillies and cut them into fine rings. Season sauce with vinegar, add chilli and bring to the boil.
Stir the starch and 1 tablespoon of water until smooth and thicken the sauce with it. Cut the strudel into about 4 pieces and arrange on plates with the sauce. You can use lamb's lettuce for example.