Creamy Potato Fennel Gratin

This gratin is exactly what a gratin should be -- rich and delectable, creamy and meltingly tender in the center, browned and crisp on the outside. I can't remember where the recipe came from at this point, but its definitely not mine -- maybe Ina Garten? Anyway, I used parmesan instead of gruyere, and next time I might use half and half or whole milk instead of the obscene quantity of heavy cream called for here. (But damn, the full-fat version was goooood.) I can't ever get enough fennel to satisfy my lust for it. We probably eat raw fennel three days out of seven; usually sliced thin over the salad at dinner, and I love its sharp bite and solid crunch. Long, slow cooking of the bulb, as in this preparation, however, turns it into a whole other comfort food experience. The potatoes are center stage here, but the slightest hint of anise flavor makes all the other flavors pop.

2 small fennel bulbs
1 yellow onion, thinly sliced
2 tablespoons good olive oil
1 tablespoon unsalted butter
2 pounds russet potatoes (4 large potatoes)
2 cups plus 2 tablespoons heavy cream
2 1/2 cups grated Gruyère cheese (1/2 pound)
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper

Preheat the oven to 350 degrees F.

Butter the inside of a 10-by-15-by-2-inch (10-cup) baking dish.

Remove the stalks from the fennel and cut the bulbs in half lengthwise. Remove the cores and thinly slice the bulbs crosswise, making approximately 4 cups of sliced fennel. Saute the fennel and onions in the olive oil and butter on medium-low heat for 15 minutes, until tender.

Peel the potatoes, then thinly slice them by hand or with a mandoline. Mix the sliced potatoes in a large bowl with 2 cups of cream, 2 cups of Gruyère, salt, and pepper. Add the sauteed fennel and onion and mix well.

Pour the potatoes into the baking dish. Press down to smooth the potatoes. Combine the remaining 2 tablespoons of cream and 1/2 cup of Gruyère and sprinkle on the top. Bake for 1 1/2 hours, until the potatoes are very tender and the top is browned and bubbly. Allow to set for 10 minutes and serve.