3 tablespoons unsalted butter, softened, plus more if needed
1 teaspoon grated lemon zest
Instructions
Cook the bacon in a large skillet over medium heat until slightly crisp, 5 to 7 minutes. Transfer to paper towels to drain then chop into small pieces. Reserve about 2 tablespoons bacon fat in the pan, increase the heat to medium high, and add the Brussels sprouts and a pinch of salt. Cook, stirring, until slightly wilted, about 3 minutes. Transfer to a bowl and toss with the bacon. Season with salt and pepper. Wipe out the skillet with a paper towel.
Place softened butter in a small bowl. Add lemon zest and stir to combine. Butter the outside of each slice of bread and place, buttered-side-down, on a clean cutting board or sheet pan.
Divide half of the cheese between 4 bread slices; top with the Brussels sprout mixture, and the remaining cheese and 4 bread slices, ending up with the buttered sides on the outside of each sandwich.
Reheat your 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.
