SWEET POTATO-RUSSET POTATO GRATIN

SWEET POTATO-RUSSET POTATO GRATIN image

Yield 8 Side dish

Number Of Ingredients 18

For the Topping
11/2 cups coarse fresh bread crumbs (from an airy crusty loaf like ciabatta)
2 Tbs unsalted butter, melted
1 Tbs Dijon Mustard
2 Tbs grated Parmesan
2 tsp chopped fresh parsley
Kosher Salt
For the Gratin
2 Tbs unsalted butter, plus 1/2 tsp for the baking dish
1 cup thinly sliced shallots
Kosher salt
2/3 cup heavy cream
2/3 cup homemade or low salt chicken broth
2 Tbsp prepared horseradish
Fresh black pepper
1 Russet potato (12 oz)
1 Sweet potato (12 oz)
1/3 cup grated parmesan

Steps:

Make the topping In a bowl combine the breadcrumbs, melted butter, and a pinch of salt. Mix in the mustard and then the Parmesan and parsley Prepare the Gratin Heat the oven to 350F. Rub a shallow 2 qt. gratin dish with 1/2 tsp butter. Melt the remaining2 Tbs butter in a small saucepan over medium heat. Add the shallots and a big pinch of salt, cook, stirring often 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. Remove from heat. Assemble the gratin Peel the potatoes, cut each in half lengthwise, and slice across into thin half moons. In a large bowl combine the sweet and russet potato slices, 2 tsp salt, the Parmesan 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. (if assembling ahead, stop now and refrigerate; bring it close to room temperature before baking) Bake the Gratin Cover with the breadcrumb topping 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 rest 15 to 20 minutes before serving