Cheesy Truffle & Spinach Burgers

Place an oven rack in the center of the oven; preheat to 450°F. Wash and dry the fresh produce. Cut the sweet potatoes into 1/2-inch rounds. Peel and thinly slice the shallot. Quarter and deseed the lemon. Grate the cheese on the large side of a box grater. In a bowl, combine the grated cheese, 2 teaspoons of cornstarch (you will have extra) and as much of the truffle zest as you'd like. Halve the buns. In a separate bowl, combine the mayonnaise, capers, and the juice of 2 lemon wedges; season with salt and pepper. Roughly chop the parsley leaves and stems.

Transfer the sweet potato rounds to a sheet pan. Drizzle with olive oil and season with salt and pepper. Toss to coat and arrange in an even layer. Roast 23 to 25 minutes, or until lightly browned and tender when pierced with a fork. Remove from the oven and evenly top with the juice of the remaining lemon wedges.

Meanwhile, in a large pan (nonstick, if you have one), heat 2 teaspoons of olive oil on medium-high until hot. Add the sliced shallot; season with salt and pepper. Cook, stirring occasionally, 1 to 2 minutes, or until softened. Add the spinach and as much of the red pepper flakes as you'd like, depending on how spicy you'd like the dish to be; season with salt and pepper. Cook, stirring frequently, 1 to 2 minutes, or until the spinach is wilted. Add the verjus (carefully, as the liquid may splatter). Cook, stirring constantly, 30 seconds to 1 minute, or until the liquid has cooked off. Transfer to a bowl and cover with foil to keep warm. Wipe out the pan.

Place the beef in a bowl. Season with salt and pepper. Gently mix to incorporate. Form the mixture into four 1/2-inch-thick patties. In the same pan, heat a drizzle of olive oil on medium-high until hot. Add the patties. Cook 4 to 5 minutes per side, or until browned and cooked through.* Leaving any browned bits (or fond) in the pan, transfer to a work surface. Carefully drain off and discard any excess oil. 

*The USDA recommends a minimum safe cooking temperature of 160°F for beef.

Working in batches, add the halved buns, cut side down, to the pan of reserved fond. Toast on medium-high 30 seconds to 1 minute, or until lightly browned. Transfer to a work surface. Wipe out the pan.

Heat the same pan on medium until hot. Add the cream (carefully, as the liquid may splatter). Cook, whisking constantly, 30 seconds to 1 minute, or until simmering. Add the cheese mixture. Cook, whisking constantly, 1 to 2 minutes, or until the sauce is thickened and smooth. Turn off the heat. Assemble the burgers using the toasted buns, cooked patties, cheese sauce, and cooked spinach. Serve the burgers with the roasted sweet potatoes on the side. Top the sweet potatoes with the lemon-caper mayo and chopped parsley. Enjoy!