3 ounces cheddar cheese, cut into ½-inch cubes, at room temperature
3 ounces Gruyère cheese, cut into ½-inch cubes, at room temperature
1 tablespoon chives, finely chopped
¼ teaspoon coarse black pepper
4 pieces sourdough bread, sliced ⅓-inch thick
2 tablespoons mayonnaise
Directions
In a food processor, combine the cheddar and Gruyère and pulse until a smooth paste forms. Transfer to a mixing bowl and fold in the chives and black pepper.
Place bread on a clean work surface. Spread a thin layer of the mayonnaise on one side of each piece of bread. Flip 2 of the slices so that the mayonnaise side faces down and use a rubber spatula or a butter knife to evenly spread the cheese over the 2 slices. Close the sandwiches with remaining 2 slices of bread, leaving the mayonnaise side facing up.
Place a large cast-iron skillet over medium heat. Add sandwiches and cook, flipping occasionally until golden brown and crispy on both sides, about 6-8 minutes.
Transfer sandwiches to a cutting board and allow them to rest for a minute before slicing in half. Serve warm.