Place 1 - 2 inches of water in a large pot with a steamer basket and bring to a boil.
Wash the Brussels sprouts. Cut off the stem end, leaving about 2/3 of the sprout and discarding the tougher outer leaves that come loose. With the tip of a knife, make an X into the interior of the core. (The trimming can be done far in advance, even a day or so if you're making for a holiday dinner.).
Transfer to the steamer tray and place over the boiling water. Cover and let steam for about 15 minutes or until cooked clear through. (I taste one to know if they're done.).
Sprinkle with the lemon juice and Parmesan. Season with salt and pepper and serve.