Cook the bacon in a large cast-iron skillet over medium heat until slightly crisp, 5 to 7 minutes. Transfer to paper towels to drain. Pour out all but 1 tablespoon drippings from the pan. Increase the heat to medium high, add the Brussels sprouts and cook, stirring, until slightly wilted, about 3 minutes. Transfer to a bowl and toss with the bacon, lemon zest, and pepper to taste. Wipe out the skillet.
Divide half of the cheese between 2 bread slices; top with the Brussels sprout mixture, and the remaining cheese and 2 bread slices. Melt the butter in the skillet over medium heat. Add the sandwiches and cook, pressing occasionally with a spatula, until the bread is toasted and the cheese melts, about 4 minutes per side, adding more butter to the pan if needed.
Photograph by Sam Kaplan
Before you slice soft cheese, chill it in the freezer for 10 to 15 minutes to firm it up.
Recipe courtesy Food Network Magazine