An easy recipe to double for a larger crowd, these ground beef sliders require no flipping over a hot grill, no utensils, and very little time prepare. Just broil them in the oven for an all-American cookout even on a rainy summer's day.
Preheat broiler with a rack in upper third. Divide beef into twelve 3-inch round patties; place on a rimmed baking sheet and season with salt and pepper. Broil until browned, about 8 minutes. Transfer to paper towels.
Switch oven to 350°F. Using a serrated knife, split rolls in half horizontally. Place bottom half on a parchment-lined rimmed baking sheet. Layer with half of cheese; top each roll with a burger patty. Layer with remaining cheese; place other half of rolls on top. Brush rolls with melted butter and sprinkle with sesame seeds. Bake until cheese is melted and rolls are lightly toasted but still soft, 8 to 10 minutes. Using toothpicks, skewer each slider with a small piece of lettuce and tomato and cornichon slices on top; serve.