Preheat the oven to 425°F with a rack in the center position.
Place the potatoes on one side of a large rimmed sheet pan. Drizzle with 1 tablespoon of the olive oil and ¼ teaspoon of the salt. Place the cabbage on the opposite side and drizzle with the remaining 1 tablespoon of olive oil and remaining ¼ teaspoon of salt. Nestle in the sausage and bake for 30-35 minutes, or until the potatoes are tender and the cabbage and sausage are lightly browned.
Meanwhile, in a small bowl, whisk together the mayonnaise or sour cream, heavy cream, vinegar, mustard, caraway seeds, dill, paprika, sugar, and garlic until combined.
Drizzle the sauce over the cabbage, sausage, and potatoes and sprinkle with fried shallots, if using.
