Make cuts (crosswise) about ⅛ inch apart, but don't cut all the way through. The chopsticks will prevent you from slicing straight through. Repeat with remaining yam halves.
Lay yam halves flat side down in a baking dish coated with cooking spray and top each half with a portion of the compound butter. Cover the dish with foil.
Roast for 40 mins, basting the yams occasionally. Uncover and roast for another 10 - 15 mins or until the yams are caramelized and can be easily pierced with a fork.