Gruyere-Crusted Root Vegetables

You can use whatever kind of root vegetables you want here: try a mix of potatoes, something assertive like turnips or rutabagas, and something sweet like beets, parsnips or sweet potatoes. If you use parsnips or sweet potatoes, be careful not to put them on the bottom, since they'll burn easily. If you're going the beet route, use golden beets or chioggia beets so you don't turn the entire dish pink. We served this with a dollop of kale pesto.

3 lbs root vegetables (we used chioggia beets, golden turnips and Yukon gold potatoes)
4 tablespoons butter
3/4 cup grated Gruyere cheese
1/2 cup grated Parmesan cheese

Preheat oven to 350. Slice root vegetables 1/8 inch thick (please, for the love of all things holy, do this with a mandoline if you've got one). Melt the butter and toss with the root vegetables in a medium-sized cast-iron skillet. Cover with aluminum foil (or a lid, if you were smart enough to register for a cast-iron skillet with a lid. Next time we get married, next time...). Bake for half an hour, then uncover and bake 10 more minutes. Sprinkle with cheese and bake another ten minutes, until bubbly and golden-brown on top.