01 - Preheat oven to 350°F or heat a large skillet over medium-low heat.
02 - Keeping the Hawaiian rolls connected, slice horizontally to create a top and bottom slab.
03 - Arrange the bottom slab on a cutting board. Evenly layer cheddar and optional Swiss cheese over the rolls. Place the top slab over the cheese.
04 - Spread softened butter evenly on the top and bottom exterior of the assembled rolls.
05 - For skillet: Place entire sandwich slab in the pan and grill 3 to 4 minutes per side, pressing gently, until crisp and cheese is melted. For oven: Transfer buttered rolls to a baking dish and bake for 10 to 12 minutes until cheese is gooey and rolls are golden.
06 - Remove from heat, let cool slightly, then cut or pull apart into 12 mini sandwiches.
07 - Optionally brush tops with Dijon mustard and sprinkle with chives or parsley before serving.