SWEET POTATO-RUSSET POTATO GRATIN

Sweet Potato-Russet Potato Gratin image

Provided by Cathy Gillespie @circlemoon8

Number Of Ingredients 18

- topping:
1 1/2 cup(s) fresh bread crumbs
2 tablespoon(s) unsalted butter, melted
- kosher salt
1 tablespoon(s) dijon mustard
2 tablespoon(s) parmigiano-reggiano, grated
2 teaspoon(s) fresh flat-leaf parsley, chopped
- gratin:
2 tablespoon(s) unsalted, butter
1 cup(s) shallots, thinly sliced
- kosher salt
2/3 cup(s) heavy cream
2/3 cup(s) chicken broth
2 tablespoon(s) prepared horseradish
- freshly ground black pepper
1 - russet potato, peeled and cut in half lengthwise, thin sliced half moons
1 - sweet potato, peeled cut in half lengthwise, thin sliced half moons
1/3 cup(s) parmigiano-reggiano, grated

Steps:

Make the topping: In a bowl, combine the breadcrumbs, melted butter, and a pinch of salt. Mix in the mustard and then the Parmigiano and parsley.
Prepare the gratin: Preheat oven 350. Rub shallow 2-quart gratin dish with butter, set aside.
Melt 2 TBS butter in a saucepan over medium heat. Add shallots and pinch of salt; cook, stirring frequently, until softened, limp and somewhat golden. Whisk together the cream, broth, and horseradish; add to the shallots. Season with salt and pepper, stir to combine, and take the pan off the heat.
Assemble the gratin: In a large bowl, combine the potato and sweet potato slices with salt, Parmigiano and the shallot cream. With a rubber spatula, mix gently but thoroughly and scrape into the prepared gratin dish, smoothing and pressing until evenly distributed.
Bake the gratin: Cover with the breadcrumbs. Bake until the crust is deep golden brown, the juices around the edges have subsided, and the potatoes are tender when pierced with a fork, about 1 hour.
Let it rest for 15-20 minutes before serving.