A grilled cheese should be perfectly crunchy on the outside and soft and gooey on the inside. This one, a grown-up version of my favorite childhood sandwich, is inspired by both an Italian antipasto plate and the English cheese toastie, with its sweet-and-sour Branston pickle. First, I make a relish by dry sautéing mushrooms (they keep a bit more freshness than when cooked in butter or oil), chopped pepperoncini, Castelvetrano olives, and a hit of citrus. Then, I sandwich it with thin shavings of extra-sharp cheddar between thick slices of sourdough miche. The fattiness of the cheese and the earthiness of the mushroom pair perfectly with the spicy peppers and salty olives. The relish is a star on its own—try it stirred into labneh as a dip or spooned alongside grilled fish or on top of roasted vegetables.
- Make the relish: Heat a cast-iron skillet over medium-low heat. Add the chopped mushrooms and dry sauté for about 4 minutes, stirring constantly to prevent sticking (they will release moisture as they cook).
- In a bowl, combine the mushrooms, pepperoncini, olives, lemon zest, and lemon juice.
- Make the sandwiches: Cut eight ½-inch-thick (1 cm) slices of bread. Using a mandoline or a very sharp knife, shave the cheese into very thin slices. Place the bread on a cutting board or sheet pan and spread ½ tablespoon butter on one side of each slice. Flip 4 slices over, buttered side down, and top each with 4 tablespoons relish, followed by cheese slices, dividing evenly. Top with the remaining 4 slices of bread, buttered side up.
- Heat a cast-iron skillet over medium heat. Cook the sandwiches until golden, about 4 minutes per side, pressing down firmly on each side with a spatula occasionally, and flipping and pressing at least twice. Sprinkle both sides of each sandwich with salt. Serve hot.