01 - Preheat oven to 350°F or set a large skillet over medium-low heat.
02 - Without separating the rolls, slice horizontally to create a top and bottom layer.
03 - Place the bottom slab on a cutting board. Arrange cheddar and, if desired, Swiss cheese evenly over the bread. Cover with the top slab.
04 - Spread softened butter evenly onto both the top and bottom exterior surfaces of the assembled rolls.
05 - For skillet: Grill the sandwich slab in the pan for 3 to 4 minutes per side, pressing gently, until golden and cheese is melted. For oven: Set the prepared rolls in a baking dish and bake for 10 to 12 minutes, until golden and cheese is gooey.
06 - Remove from heat, let stand briefly, then slice or pull apart into 12 mini sandwiches.
07 - Optionally, brush with Dijon mustard and sprinkle with chopped chives or parsley before serving.