Mornay and Mushroom Duxelles Burger w/Crispy Shallots

By stancec44

Using 80-precent lean ground beef guarantees juicy, flavorful burgers.
Handling the ground beef as little as possible and only seasoning the exterior creates a patty with a perfect hamburger texture that isn't tight like meatloaf.
Mushroom duxelles add an intense mushroom flavor, and stay put on the burger more easily than sliced sautéed mushrooms do.

Ingredients

• 3 medium shallots, roughly chopped
• 20 ounces cremini mushrooms, roughly chopped
• 4 1/2 tablespoons unsalted butter, divided
• 1 tablespoon loosely packed fresh marjoram leaves, finely chopped
• Kosher salt and freshly ground black pepper
• 1 1/2 tablespoons all-purpose flour
• 1 cup milk
• 3/4 cup grated Gruyere cheese (about 4 ounces)
• 1 1/2 pounds freshly ground beef chuck, preferably about 80 percent lean, formed into 4 (4 1/2 inch wide) patties
• 4 onion rolls, split and toasted
• 1 recipe Thai-Style Fried Shallots
• 2 cups thinly sliced shallots
• 2 cups vegetable oil
• Kosher salt

Preparation

Step 1

FOR THE SHALLOTS (makes about 1 cup):
Line a large plate or rimmed baking sheet with 8 layers of paper towels. Set a fine mesh strainer over a large heat-proof bowl or medium saucepan. Combine shallots and oil in a wok or medium saucepan. Place over high heat and cook, stirring frequently, until shallots begin to bubble. Continue cooking, stirring constantly as the shallots fry to ensure even cooking. When shallots are light golden brown, transfer to strainer and drain. (Shallots will continue cooking for a brief period after draining, so don not allow them to get too dark). Immediately transfer to paper towel-lined tray and season with salt. Allow shallots to drain, then carefully lift the top layer of paper towels and roll shallots onto second layer, blotting gently with the first. Repeat, until shallots are on the last layer of paper towels and mostly grease-free. Allow to cool to room temperature, then store in an airtight container at room temperature for up to 3 months.

FOR THE BURGER:
In a food processor, process shallots until minced, then scrape into a small bowl. Add mushrooms and process until minced, scraping down sides as necessary. Heat 3 tablespoons butter in a medium pot over medium-high heat until foaming. Add shallots and cook, stirring, until tender, about 3 minutes. Add mushrooms and cook, stirring, until water has released and evaporated, about 3 minutes. Continue to cook mushrooms, scraping up browned bits from bottom frequently, until darkened and fragrant, about 8 minutes. Stir in marjoram, season with salt and pepper and cook mushroom duxelles for 1 minute longer. Set aside.

In a small saucepan, heat remaining 1 1/2 tablespoons butter with flour over medium-high heat until butter has melted and formed a paste with flour. Continue to cook, stirring, until raw flour scent is gone, about 1 minute. Whisk in milk until smooth and cook, whisking, until sauce comes to a simmer and begins to thicken slightly. Lower heat to low and cook, stirring, until sauce is thick enough to coat back of a wooden spoon, about 3 minutes. Whisk in cheese until smooth, moving saucepan on and off heat to keep it hot enough to melt cheese but not so hot that it bubbles rapidly. Season Mornay sauce with salt and pepper and set aside.

Season patties generously with salt and pepper. Cook to desired doneness on a hot grill or in a skillet on the stovetop, 125°'F for medium rare or 135°'F for medium. Transfer to a plate and allow to rest for 5 minutes.

Rewarm mushroom duxelles and Mornay sauce if necessary. Spread mushroom on bottom bun halves, top with patties, then spoon sauce on top. Sprinkle fried shallots all over, close hamburgers, and serve immediately.