01 - Preheat oven to 350°F. Line a baking sheet with parchment paper.
02 - Without separating the rolls, slice the whole block horizontally to create top and bottom halves.
03 - If using, whisk Dijon mustard and mayonnaise together. Spread evenly onto cut sides of the rolls.
04 - Layer cheddar cheese evenly over bottom half. Place top half over cheese to reassemble.
05 - Place assembled rolls on baking sheet. Brush tops generously with melted butter. Sprinkle with garlic powder and dried parsley if desired.
06 - Cover loosely with foil and bake for 10 minutes.
07 - Remove foil and bake 5 additional minutes until cheese is fully melted and tops are golden.
08 - Let rest 2 minutes, then cut apart into 12 mini sandwiches. Serve warm.