CASSEROLE DISH: 9x13-inch baking dish
BAKE TIME: 1 hour
2 small fennel bulbs, trimmed
2 large leeks
2 large russet potatoes (between 3/4 and 1 pound), peeled
1 large onion, thinly sliced
4 cloves garlic, minced
1 cup sour cream
1 teaspoon salt
1/2 teaspoon ground nutmeg
1/4 teaspoon freshly ground black pepper
1 cup grated Grana Padano cheese
Preheat the oven to 400°F. Lightly grease the baking dish with olive oil.
Using a mandoline or very sharp knife, cut the fennel bulb into thin slices. (Note: I aim for about 1/8-inch thick slices. A mandoline or food processor is almost mandatory for this.) Cut each leek in half lengthwise and rinse to remove any grit; pat dry. Slice the leek halves into 1-inch-wide half moons and separate each layer. Slice the potatoes as thin as the fennel (just use the same setting on the mandoline or food processor), and toss all these vegetables into your largest bowl with the onion and garlic.
Stir in the sour cream, salt, nutmeg, pepper, and cheese. The mixture will be thick and just barely covered with the cheese and sour cream. Scrape into the prepared baking dish and cover tightly with foil. (This amount of vegetables will pack the baking dish very full — but after baking it, the volume will go down considerably.)
Bake for 45 minutes, then remove the foil and bake for an additional 15 minutes to let the top brown. Let stand for 10 minutes, then serve hot in big scoops.
Recipe Notes:
• I like to add some fresh herbs to this as well, if they are on hand. Some snippets of the fennel fronds are nice, or a few snipped sorrel leaves. I also like to garnish the top of the gratin with more of the feathery fennel fronds when serving.
• If you can't find Grana Padano (here's a primer on this cheese) use another hard, salty cheese like Parmesan or aged Asiago.
• On the sour cream: I have only made this with full-fat sour cream. I would not recommend using lower-fat sour cream, but you're welcome to try. There's only 1 cup in this entire casserole, so I think using a higher-fat product is better here.
This recipe had been updated - originally published April 2011.