Potato-horseradish gratin with caramelized onions

Potatoes, medium sized	2 ½ pounds
Salt	½ teaspoon + ½ teaspoon
Pepper, freshly ground	½ teaspoon + ½ teaspoon
Half-and-half	2 cups
Horseradish, cream style	½ cup
Butter, unsalted	¼ cup
Onions, large, thinly sliced	2
Sugar	1 teaspoon
Balsamic vinegar	1 tablespoon
Swiss cheese, grated	6 ounces
Parsley, freshly chopped	¼ cup + ¼ cup

1. Preheat oven to 400°F. Lightly grease a 13-by-9-inch baking dish.
2. Place potatoes in pot and fill with water until covered; boil for 20 minutes, or until almost tender.
3. Drain, and cool slightly; peel potatoes, and cut in 1/4-inch-thick slices.
4. Arrange potato slices in dish, sprinkling with 1/2 teaspoon salt and pepper as you layer.
5. Stir together half-and-half and horseradish, and poor over potatoes.
6. Cover, and bake for 40 minutes.
7. Meanwhile, melt the butter in a large skillet over medium heat.
8. Add the onions, and remaining salt and pepper; stir occasionally, and cook for 20 minutes.
9. Sprinkle the sugar over the onions, and continue cooking and stirring for another 5 to 8 minutes, or until the onions are caramel in color.
10. Stir in vinegar, and cook 2 minutes, or until the liquid evaporates.
11. Remove from heat, and cool 5 minutes.
12. Fold in cheese, and half of the parsley.
13. Uncover the potatoes, and top with the onion mixture.
14. Reduce the oven to 350°F, and bake for 30 minutes.
15. Let stand 5 minutes, and then sprinkle with the remaining parsley.

Recipe from Southern Living 1001 Ways to Cook Southern.