In a deep-fryer or heavy-bottomed pot, heat enough canola oil to come halfway up the sides of the pot, to 375 degrees F.
Preheat a grill on medium-high.
In a large skillet over medium-high heat, add the butter. Stir in the onions and cook until translucent, about 1 minute. Add the cabbage and cook until softened, about 3 to 4 minutes. Season the cabbage with salt, pepper, and crushed red pepper, to taste. Add the sugar, cider and stock. Cook until the cabbage is al dente, about 6 to 8 minutes
In a small bowl, mix together the sour cream, shallot, lemon zest, lemon juice, cayenne and chives. Season the cremolata with salt and pepper, to taste.
Add potato peels to the fryer and fry until crisp, about 3 minutes Remove to a paper towel lined platter and season with salt and pepper, to taste.
Grill the bratwurst, turning frequently until cooked through, about 8 to 10 minutes
Open the rolls and spread with some of the sour cream cremolata. Add the sausage and some warm braised cabbage. Top each with some crispy potatoes and finish with a little more cremolata before serving.