Place the cabbage, onion, cider, cider vinegar, brown sugar, 1/4 cup ketchup, the juniper berries, if using, allspice berries, mustard, coriander and caraway seeds and bay leaf in a medium size pot. Season liberally with salt and pepper and bring to boil. Reduce the heat and partially cover; cook until the cabbage is very tender and the flavor develops, 25-30 minutes, stirring occasionally.
Heat a grill pan or griddle over medium-high heat.
Simmer the fresh sausages in an inch of water to cook them through. If they are cooked brat,wurst skip this step. Butterfly the bratwursts so they open like a book. Griddle on both sides with a drizzle of oil until crispy and brown. Wipe the griddle clean.
Combine sour cream, the remaining 1/4 cup ketchup, relish, fresh herbs, salt and pepper in a small bowl.
Spread the bread on one side lightly with butter. Dress the other side of the bread with the sauce and layer the cheese, sausage, cabbage, cheese and bread, with the buttered sides facing out. Grill the sandwiches over medium heat until crispy and brown and the cheese melts.