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Cheesy Onion and Potato Gratin

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[Photographs: J. Kenji Lopez-Alt]

Wanna know the real secret to a successful, happy marriage? Plenty of melted cheese and crisp crusts. Communication and mutual understanding come in a distant second and third.

My wife is the kind of woman who likes to gift a doting husband with really pretty ceramic casserole dishes. Serendipitously, I'm the kind of kind who likes being gifted with these dishes. Even luckier still, it is almost sheer coincidence that I enjoy cooking in these dishes and that she enjoys eating what is cooked in them.

As such, I'm constantly trying to figure out new delicious things to cook in them. Here's a recent favorite: tiny new potatoes and pearl onions baked together with crisp bacon lardons, melted Comté cheese, and a crisp, garlicky bread crumb crust on top. The tender potatoes pop in your mouth in flavorful bursts, while the onions become sweet and tender. The whole thing is vaguely reminiscent of a traditional raclette, but with a crisp crust and cleaner presentation to bump things up a bit.

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Start by cooking the potatoes. Tiny new potatoes are my favorite because they can be baked with their skins intact, softening up until they pop almost like little balloons (or giant beads of caviar), though chunks of larger potatoes will also work. Start the potatoes in cold salted water for the most even cooking.

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I tried par-cooking pearl onions to various degrees and found that the dish worked best when the onions were almost raw going into the dish. Just a moment in boiling water to loosen the skins and begin the cooking process is enough.

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If you trim off the top and bottom of the onions and score a very faint X into one of the cut sides, the skins should be really easy to peel off after blanching and cooling.

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Next element: the bacon. I use slab bacon cut into thick lardons so that you get a nice contrast between crisp crust and juicy, meaty center when you bite into one. To cook them, the best way is to place them in a saucepan and cover them with a little water before heating. That way, the water gets the rendering process going a bit and softens up the pork.

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Eventually, the water evaporates, leaving you with a slick of rendered bacon fat to cook your lardons in.

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Crisp and golden brown is what we're after.

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Everything gets tossed together with just a drop of cream to bind the drippings into a sauce, along with some chopped parsley to freshen things up.

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I told you my casserole dishes are pretty, didn't I?

I pile all the onions and potatoes into the dish, then top it off with a good amount of grated Comté cheese. Gruyère or any aged Swiss alpen-style cheese will work here. You want something with a nice nutty flavor and good melting characteristics.

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It gets a brief par-bake in the oven. Why? To help some of the fat in the cheese and cream separate out. It looks greasy and, frankly, a little gross coming out of the oven after its first trip, but that fat all serves a purpose: to coat the seasoned bread crumbs you're going to add.

Once the bread crumbs soak up some of that fat, they brown and crisp in the oven, producing a nice crunchy crust that's a great contrast to the gooiness underneath.

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What's that dear? You don't eat bacon? Ah well, I suppose I'll have to finish this one all by myself then.

About the author: J. Kenji Lopez-Alt is the Chief Creative Officer of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.

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