Place the pretzel sticks on a lightly floured baking paper and allow to defrost.
In the meantime, cut the sausage into very thin slices at an angle. Cut the onion into fine half-rings. Roughly chop the arugula. Finely slice the radishes. Mix the ingredients for the sauce until smooth and season with salt and pepper.
Cut the pretzel sticks in half. Place 3 halves next to each other, dust lightly with flour and flatten with a rolling pin to form a large flatbread (see picture below). Sprinkle both loaves with sesame seeds and bake in an oven preheated to 200 degrees Celsius for about 12-15 minutes. Remove the pretzel rolls from the oven and leave to cool slightly.
Meanwhile, fry the sausage in a pan with a dash of vegetable oil at high temperature until crispy. Cut open the buns and put some sauce in first. Then top with sauerkraut, arugula, bratwurst sausage, onions and radishes. Finally, top with some more sauce.