Preheat oven to 425°F.
Combine Parmesan, butter, garlic salt and pepper in medium bowl.
Sprinkle cheese mixture in an even layer over a nonstick rimmed baking sheet.
Press Brussels sprouts, cut-sides-down, into cheese mixture in a single layer about 1-inch apart.
Bake until Brussels sprouts are tender, and cheese is light golden-brown about 15 to 18 minutes.
Let sit at room temperature for at least 5 minutes before gently separating Brussels sprouts.
Meanwhile, combine sour cream, Parmesan, mustard, chives, garlic and pepper in a small bowl.
Serve with Brussels sprouts and enjoy.
