Truffle Umami Blast Burgers

Once potatoes have roasted 15 minutes, remove from oven and push to one side of sheet. Mound Parmesan on empty side in two even piles. (For 4 servings, leave potatoes roasting and add cheese to a second sheet; bake on middle rack.) Return to oven and bake until cheese is melted and crispy at edges and potatoes are tender, 5-7 minutes more. Let frico cool for 1 minute on sheet, then transfer to a plate.

Meanwhile, trim and thinly slice mushrooms. Heat a large drizzle of oil in a large, preferably nonstick, pan over medium-high heat. Add mushrooms; cook until golden brown, 3-4 minutes. Add remaining shallot; cook, stirring, until softened, 2-4 minutes. Stir in ¼ cup water (⅓ cup for 4 servings) and stock concentrate; cook until liquid has mostly evaporated, 1-2 minutes. Season with salt and pepper. Turn off heat; transfer to a plate. Wipe out pan.

Meanwhile, halve buns. In a medium bowl, combine beef and ¼ tsp truffle zest (½ tsp for 4 servings; you’ll use more later). Season generously with salt and pepper. Form into two equalsized patties (four patties for 4), each a bit wider than a burger bun.

Heat a drizzle of olive oil in pan used to cook mushrooms over medium-high heat. Add patties and cook to desired doneness, 3-5 minutes per side. Meanwhile, in a second small bowl, combine mayonnaise, sour cream, ¼ tsp truffle zest (½ tsp for 4 servings), salt, and pepper. (Taste and add more truffle zest if desired.) Toast buns until golden.