In a soup pot, heat 1 tablespoon EVOO, 1 turn of the pan, and the 2 tablespoons butter over medium to medium-high heat. Add the potatoes and onion, season with salt and pepper and cook for 7 minutes. Add the cabbage, carrots and bay leaf and cook for 5 minutes. Stir in the beer, dill, parsley and caraway seeds and cook for 1 minute. Stir in the chicken broth and mustard, bring to a simmer, then lower the heat and keep warm.
In a large skillet, combine the knockwurst, bratwurst and remaining 1 tablespoon EVOO with enough water to fill the skillet by 1/4 inch. Cook over medium-high heat until the liquid evaporates and the sausages brown, 12 to 15 minutes. Cut the sausages into 2-inch chunks.
Toast the bread, then lightly butter and cut into strips.
Top the stoup with the knockwurst and bratwurst. Serve with the toasts.