01 - Preheat the oven to 350°F or heat a large skillet over medium-low heat.
02 - Without separating the Hawaiian rolls, slice them horizontally to form a top and bottom slab.
03 - Position the bottom slab on a cutting board. Arrange cheddar cheese slices—add Swiss cheese if desired—covering the rolls evenly. Place the top slab back over the cheese layers.
04 - Spread the softened butter evenly across the top and bottom exterior of the assembled rolls.
05 - For skillet preparation: grill entire sandwich slab for 3 to 4 minutes per side, gently pressing, until both sides are golden and cheese is melted. For oven method: transfer the buttered rolls to a baking dish and bake for 10 to 12 minutes until the cheese is gooey and the bread is golden.
06 - Remove from heat, allow to cool slightly, then cut or pull apart into 12 individual mini sandwiches.
07 - If desired, brush the tops with Dijon mustard and sprinkle with chopped chives or parsley before serving.