Drain the sauerkraut. Heat 1 tablespoon butter in a saucepan. Add the sauerkraut and sauté briefly. Add 2 tablespoons of sugar and caramelize lightly. Season with salt and pepper, add the bay leaf, caraway seeds and juniper. Fill up with apple juice and reduce to a medium heat for about 20 minutes.
In the meantime, cut the onions into fine strips. Heat the rest of the butter in a pan and stir the onions in it over a medium heat, stirring occasionally, simmer until golden in about 10-15 minutes. Season with salt, pepper and a pinch of sugar.
Pluck tarragon leaves, roughly chop and add to the mayonnaise. Mix in the mustard and horseradish and season with salt and pepper. Cut the bell pepper into rings.
Heat oil in a pan. Fry the sausages on all sides until crispy. Halve the pretzel rolls horizontally and bake in the preheated oven.
Spread the mayonnaise and sauerkraut on the buns. Top with the pointed peppers, sausages and onions. Finish with the bread roll lids.