Place the cabbage in a large kettle, and add the diced apple, 2 teaspoons of the salt, lemon juice, and 1/2 cup water. Bring to a boil then simmer, covered, about 15 minutes stirring occasionally.
In hot butter, saute the onion until golden. Add the onion to the cabbage along with 1 teaspoon salt, pepper, vinegar and sausage. Cook, covered, 20 to 30 minutes until sausage is heated through. To serve, spoon the cabbage onto a heated platter, topping it with the sausage.
