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.