- 3 1/2 cups heavy cream
- 2 garlic cloves, minced
- 1 3/4 teaspoons salt
- 1/2 teaspoon freshly ground pepper
- About 6 tablespoons grated peeled fresh horseradish root
- 2 1/2 pounds Idaho potatoes (about 5), peeled and thinly sliced
- 1/2 large tart apple, such as Granny Smith—peeled, halved, cored and thinly sliced
- 1/4 cup freshly grated Parmesan cheese
- In a medium bowl, combine the heavy cream, garlic, salt and pepper. Gradually stir in the horseradish, tasting for strength.
- In a 13-by-9-inch nonreactive baking dish, layer the potatoes and apple. Pour the horseradish cream over the potatoes. Bake in the upper third of the oven for about 30 minutes, or until bubbling. Sprinkle the Parmesan cheese over the top and bake for about 15 minutes longer, or until the potatoes are tender and the top is nicely browned. Cover the gratin with foil and let stand in a warm place for 10 to 30 minutes before serving. Cut the gratin into 8 squares with a pie server.
The potatoes can be prepared through the point where horseradish cream is poured over them up to 2 hours ahead. Do not refrigerate.