Potato-Horseradish Gratin with Caramelized Onions

I first made this recipe on February 25, 2012. I know this because the menu for that dinner party is still the bookmark on page 862 of Southern Living's 1001 Ways to Cook Southern, a gift I received from my now mother in law when Brian and I moved to North Carolina from Massachusetts the summer of 2011. That February dinner party night I served a Rosemary-Thyme Rib Roast. Potato gratin has since made its way to my Easter table. Last year there wasn't time for this more involved version of the dish, and I went a more classic route. This year I am trying it as a make ahead dish - I'll let you know how that works out when I edit to add pictures in a couple days!

Potato-Horseradish Gratin with Caramelized Onions

from Southern Living's 1001 Ways to Cook Southern
makes 8 servings   ||   prep: 1 hr, 25 min. cook: 1 hr., 10 min. stand: 10 min.

Ingredients:

2 1/2 lb medium-size baking potatoes

1 tsp salt, divided

2 cups half-and-half

1/2 cup cream-style horseradish

1/4 cup butter

2 large onions, thinly sliced

1 tsp sugar

1 tbsp balsamic vinegar

1 cup (4 oz) shredded swiss cheese

1/4 cup chopped fresh parsley, divided

Directions:

1. Preheat oven to 400°F. Cook potatoes in boiling water to cover 20 minutes or until almost tender. Drain and cool slightly. Peel potatoes, and cut into 1/4-inch-thick slices. Arrange potato slices in a lightly greased 13-x 9-inch baking dish. Sprinkle with 1/2 tsp salt and 1/2 tsp pepper. 

2. Stir together half-and-half and horseradish, and pour over potato.

3. Bake, covered, at 400°F for 40 minutes. 

4. Melt butter in a large skillet over medium heat. Add onion, remaining 1/2 tsp salt, and remaining 1/2 tsp pepper; cook, stirring occasionally, 20 minutes. Add sugar and cook, stirring occasionally, 5-8 minutes or until onion is caramel colored. 

5. Stir in vinegar, and cook 2 minutes or until liquid evaporates. Remove from heat, and cool 5 minutes. Fold in cheese and 2 tbsp of parsley. 

6. Uncover potato; top with onion mixture. Reduce temperature to 350°F. 

7. Bake at 350°F for 30 minutes. Let stand 5 minutes; sprinkle with remaining 2 tbsp parsley. 

Make ahead option: 

This can be prepared through step 5 up to 24 hours before. Remove potatoes from oven, let cool. Keep covered and refrigerate. Cover onion mix and refrigerate. 

When ready to cook, remove from fridge and allow to come back towards room temperature 30-60 minutes. Top potato with onion mixture and cook uncovered at 350°F for 30-40 minutes or until heated through. Finish with parsley as normal. 

What is your favorite make-ahead holiday meal? Favorite holiday potato?