Place potatoes in large pot of salted water. Bring to boil over high heat, reduced to medium-high and cook covered 30 to 35 minutes or until just fork tender. Remove from heat and drain.
Lightly grease rimmed baking sheet. Pat potatoes dry and arrange on baking sheet. Using potato smasher or bottom of small bowl, gently smash potatoes, leaving in one piece.
Turn on oven broiler to high. Place oven rack on upper middle setting. (not all the way to the top)
In small bowl, whisk together butter, garlic, parsley, rosemary and thyme. Spoon mixture evenly over each potato. Lightly sprinkle with salt and pepper.
Set baking sheet in oven and broil potatoes until crispy and golden, about 12 to 15 minutes. Remove pan from the broiler, sprinkle with grated parmesan and return to broiler until cheese is starting to crisp, about 2 to 3 minutes.