Bring a medium pot of water to a boil and add 2 teaspoons salt.
Add the Brussels sprouts and cook for exactly 5 minutes. Drain.
Heat the broiler to high with a rack placed 6 inches from the heat source.
Transfer the sprouts to a large rimmed baking sheet. Toss with the oil and the parmesan.
Place under the hot broiler until the sprouts are golden and the cheese is bubbling, about 5 minutes depending on the power of your broiler. Rotate the pan and stir the sprouts around about halfway through.
Sprinkle with salt and serve.
If your Brussels sprouts are more than 1-inch in diameter, slice them in half.Make sure to set your timer for the par-boiling step - overcooking the Brussels sprouts will turn them dark green and mushy.