01 - Preheat oven to 350°F or warm a large skillet over medium-low heat.
02 - Using a bread knife, slice the rolls horizontally as a single slab, keeping the rolls connected.
03 - Place the bottom half of the rolls on a cutting board. Arrange halved cheddar slices evenly across the surface, adding Swiss cheese if desired. Cover with the top slab of rolls.
04 - Evenly spread softened butter over the exterior top and bottom of the assembled rolls.
05 - For skillet: Place the roll slab in the pan and cook, pressing gently, 3–4 minutes per side until golden and the cheese is melted. For oven: Transfer buttered rolls to a baking dish and bake 10–12 minutes, until bread is golden and cheese is gooey.
06 - Let rest briefly. Cut or separate into 12 mini sandwiches. Optional: Brush tops with Dijon mustard and sprinkle with chives or parsley before serving.