Sunchoke & Sweet Potato Gratin

Today, instead of going to our usual Sunday's Farmer's Market in Temescal we trekked out to the larger one at Grand Lake in Oakland. It's a 25 minute bike ride instead of our usual 10 minute walk, but there's always some more unique finds at the larger market.

This week, we came across some sunchokes and early season white sweet potatoes. For those who have never seen a sunchoke, they are these kind of nubbly tubers and have nothing to do with an artichoke (though often they are labeled "Jerusalem Artichokes"). I've roasted sunchokes before and while they're delicious prepared that simply, we were looking for something just a bit more interesting.

Note, this recipe is VERY heavy so you definitely should eat it in moderation and be in the mood for such a thing

I decided to adapt one of my favorite gratin recipes to include sunchokes, but omit the greens.

Ingredients
2 lbs sunchokes, roughly peeled and thinly sliced
2 medium sweet potatoes, peeled and thinly sliced
1 onion, diced
1 tablespoon olive oil
2 gloves garlic, minced
1 cup heavy cream & 1 cup whole milk (Or any 2 cup combination of the two)
2 tablespoons butter + more for the dish
2 tablespoons flour
5 oz gruyere cheese, coarsely grated (a little over a cup)
fresh thyme
fresh rosemary
salt
pepper

1. Preheat the oven to 400 degrees. Over medium heat heat the olive oil. When hot, sauté the onions until soft and translucent then set aside.

2. Make the sauce. In a small sauce pan over low heat heat the garlic, cream, milk, and a pinch of salt just until barely simmering. In a separate pan, melt the butter over low heat.

3. When the butter is melted, sprinkle in the flour and whisk for about a minute. Whisk in the warmed milk/cream mixture for another minute or two until the mixture starts to thicken.

4. Butter a 9x13 baking dish. Spread half of the sweet potatoes and then half the sunchokes on the bottom of the pan. Next, sprinkle half of the onions on top followed by half of the sauce and then half the cheese. Sprinkle some salt and pepper over the top.

5. Make the next layer by spreading the potatoes, then the sunchokes, then the remaining onions, then the remaining sauce, then the cheese, another bit of salt and pepper.

6. Cook until most of the liquid has rendered out and the cheese is bubbly and browned (about an hour).