Heat 2 teaspoons oil in a large skillet over medium heat. Add onion and cook, stirring, until beginning to brown, about 5 minutes. Stir in caraway (or fennel) seeds and cook until fragrant, about 30 seconds. Add apple and wine; increase heat to medium-high and cook, stirring, until most of the wine has evaporated, about 5 minutes. Stir in sausage, sauerkraut, vinegar, mustard and pepper. Transfer to a 9-by-13-inch (or similar 3-quart) baking dish.