HORSERADISH MASHED POTATOES WITH CARAMELIZED ONIONS

Horseradish Mashed Potatoes with Caramelized Onions image

Yield Serves 6

Number Of Ingredients 7

1/4 cup plus 6 tablespoons (1 1/4 sticks) butter
2 1/4 pounds white onions, thinly sliced
3 tablespoons balsamic vinegar
2 teaspoons chopped fresh thyme
3 1/2 pounds russet potatoes, peeled, cut into 1-inch pieces
6 to 8 tablespoons whole milk
1/4 cup prepared white horseradish

Steps:

Melt 1/4 cup butter in large skillet over medium heat. Add onions; sauté until deep golden, about 30 minutes. Add vinegar and thyme. Reduce heat to low; sauté 4 minutes. Season with salt and pepper.
Meanwhile, cook potatoes in large pot of boiling salted water until very tender, about 20 minutes. Drain. Return to same pot; mash until smooth. Add 6 tablespoons milk, horseradish and 6 tablespoons butter; stir to blend. Thin with 2 tablespoons milk if necessary. Season with salt and pepper.
Transfer potatoes to serving dish. Spoon onion mixture atop potatoes. (Can be prepared 8 hours ahead. Cover with foil and refrigerate. Rewarm in 350°F oven about 30 minutes.) Serve hot.