Scalloped potatoes are great, but you know what's even better?! Creamy celery root and sweet potato smothered in a cheesy cream sauce and topped with crispy bread crumbs. Bring this Celery root and sweet potato gratin to your next family dinner and wait for the praise to roll in!
Celery Root & Sweet Potato Gratin
1 quart milk
1 quart heavy cream
3 garlic cloves, thinly sliced
Salt & freshly ground pepper
2 large celery roots (about 2 1/2 pounds)—peeled, halved and very thinly sliced on a mandoline
4 medium sweet potatoes (about 21/2 pounds) peeled and very thinly sliced on a mandoline
6 slices of thick-cut bacon, finely chopped
1 medium white onion, coarsely shredded
2 large Granny Smith apples, coarsely shredded
1 T chopped thyme
3 c coarsely shredded Gruyère cheese
3 T panko (Japanese bread crumbs)
In a large pot, bring milk & cream to a boil with the garlic. Season with salt & pepper. Add celery root & sweet potatoes & cook, stirring occasionally, until slightly softened, about 2 min. Remove from heat & let cool for about 20 min. Drain sweet potato and celery root in a colander set over a large bowl, reserve cooking liquid.
In a medium skillet cook bacon over moderately high heat until crisp. Drain & transfer to a medium bowl. Squeeze out as much liquid as possible from grated onion & apples, then add to the bacon. Add thyme, stir to combine.
Preheat oven to 350°. Butter a 2 1/2-to 3-quart shallow baking dish. Arrange one-third of the celery root and sweet potatoes in an even layer. Spread half of the onion-bacon-apple mixture on top and season lightly with salt & pepper. Sprinkle with one-third of the cheese. Repeat layering once more then top with remaining celery root & sweet potatoes & the remaining cheese. Pour enough cooking liquid over the gratin to reach the top of the dish. Sprinkle with panko & cover with buttered sheet of foil.
Bake the gratin in the center of the oven for 45 minutes. Remove the foil and bake for about 45 minutes longer, until bubbling and golden. Let rest for at least 30 minutes before serving.