01 - Preheat oven to 350°F or heat a large skillet over medium-low heat.
02 - Without separating, slice the Hawaiian rolls horizontally to create a top and a bottom slab.
03 - Place the bottom slab on a cutting board and evenly layer the halved cheddar and optional Swiss cheese over the surface. Cover with the top slab.
04 - Spread softened butter evenly onto the outside top and bottom of the assembled rolls.
05 - For skillet: Place assembled rolls in skillet, grilling 3–4 minutes per side while pressing gently, until golden and cheese is melted. For oven: Transfer to a baking dish and bake 10–12 minutes until bread is golden and cheese is gooey.
06 - Remove from heat, let cool slightly, then separate into 12 mini sandwiches.
07 - Optionally, brush with Dijon mustard and sprinkle chopped chives or parsley before serving.