01 - Preheat oven to 350°F or heat a large skillet over medium-low heat.
02 - Without separating, cut the Hawaiian rolls in half horizontally to form a top and bottom slab.
03 - Place the bottom slab on a cutting board and evenly layer cheddar cheese, and Swiss cheese if desired, over the rolls. Cover with the top slab.
04 - Spread softened butter evenly on the exterior top and bottom of the assembled rolls.
05 - For skillet: Place the sandwich slab in the pan and grill for 3 to 4 minutes per side, pressing gently, until golden and cheese melts. For oven: Set rolls in a baking dish and bake for 10 to 12 minutes, until the cheese is gooey and the bread turns golden brown.
06 - Remove from heat, allow to cool slightly, then slice or pull apart into 12 mini sandwiches.
07 - Brush with Dijon mustard and sprinkle with chives or parsley before serving, if desired.