1. Bring a large pot of heavily salted water to a boil. Add the penne pasta and cook according to package directions.2. Two minutes before the pasta is al dente, add the broccoli florets to the pot.3. While the pasta cooks, heat the olive oil in a large skillet over medium heat. Add the minced garlic and red pepper flakes and cook for 1 minute until fragrant.4. Pour in the broth and let it simmer for 1 minute.5. Just before draining the pasta, reserve 1 cup of the starchy pasta water.6. Use a spider or slotted spoon to transfer the pasta and broccoli directly into the skillet with the sauce.7. Add the Parmesan cheese, mozzarella cheese, and 1/2 cup of the reserved pasta water to the skillet.8. Stir and toss vigorously over medium heat for 1-2 minutes, until the cheese is melted and the sauce becomes creamy and coats the pasta. Add more pasta water, 1 tablespoon at a time, if the sauce is too thick.9. Season with salt and pepper to taste. Serve immediately.