Cook penne according to package instructions al dente.
Place the broccoli florets in a colander and slowly drain the pasta over the broccoli. This will help to quickly cook the broccoli, set pasta and broccoli aside.
Melt the butter in a large, deep skillet over medium heat. Add lemon juice, penne, and broccoli. Season with salt and pepper to taste.
Let mixture warm through, stirring occasionally for 5 minutes. Garnish with parmesan cheese and additional lemon juice if desired.