Burger Toppings Week: Insane Mornay and Mushroom Duxelles Burger

"Eating this is what making out with Escoffier would be like."

I think it's safe to say that before my esteemed colleague Max spoke these words, I'd never considered what making out with Escoffier might have been like. As soon as he said it, though, I somehow knew it was true. There's just something about this burger that seems...postcoital. I feel dirty just looking at it.

I wasn't trying to channel sweaty rumpled sheets when I first started working on this thing. But clearly what started out as an innocent attempt at a burger with French flavors ended up more along the lines of a French kiss. I think maybe that means I got it right.

French food goes in and out of style every few years, at least in the trendisphere, with food glossies declaring the return of la grande cuisine on the semi-regular. There's actually some truth to it, as many of the world's other great culinary traditions have grown in popularity and the hot spots of innovation have shifted, eclipsing what was once France's near-singular grasp on the Western food imagination.

All of this is to say that, of all the sources of burger-topping inspiration out there, France, at least in my experience, is pretty far down the list. I'm not saying that no one has ever done a French burger, but it's definitely not common. And yet there are so many good ideas to plumb!

Take, for example, the mushroom duxelles here. Mushrooms on burgers are definitely nothing new. But the usual suspects are either a giant portobello cap or sliced sautéed 'shrooms. Those can be good, but I wasn't convinced that they're the best way to add mushroom flavor to a burger. Meaty and juicy, a good burger doesn't need to double down on those qualities with a slab of portobello. Meanwhile, sautéed sliced mushrooms have a structural deficiency: they tend to slide off the burger too easily.

Duxelles is my answer. A mixture of minced mushrooms sautéed with shallots, duxelles is like a spread, almost creamy and pâté-like in texture. They add a new texture that's soft and creamy, and, because they're minced and cooked down until concentrated, their mushroom flavor is intense, almost raunchy.

A surprise benefit: For anyone who, whether for reasons of preference or autoimmune necessity, must eat a well-done burger, duxelles manage to introduce a juicy, rare-meat quality back to the burger to counter what would otherwise just be overly dry, crumbly beef. Don't get me wrong: I'm not recommending overcooking your burgers, I'm just saying duxelles have a way of offsetting the effect if you do.

To add yet another level of inappropriateness, I went overboard indulgent with the sauce, a classic Mornay, which is béchamel loaded with melted Gruyere cheese. There are a lot of good tricks for making awesome cheese sauce, including Kenji's hack made with cornstarch and evaporated milk, but in a pinch, Mornay is freaking excellent and easy as can be: You just make a basic béchamel, and then whisk in handfuls of grated cheese until smooth. The only real risk is if you overheat the sauce once the cheese has been added, in which case it can break and lose its perfect texture. I like to whisk in the cheese off the heat, only returning it to the flame if it's cooled down too much to allow the full amount of cheese to melt into it.

To cap the whole thing off, I added some fried shallots for crunch and to underscore the flavor of the shallots in the duxelles, and served my burgers on tender onion rolls, just to drive that toasted onion flavor home even more.

The whole thing is enough to make Escoffier roll in the grave hay.