Boil a large pot of salted water. Add penne pasta and cook until al dente (about 8-10 minutes). Toss in broccoli florets 2 minutes before draining.

Heat olive oil in a large skillet over medium heat. Add minced garlic and cook for 30 seconds until fragrant.

Sprinkle in flour and whisk for 1 minute until the mixture begins to bubble.

Slowly pour in vegetable broth and heavy cream while whisking. Simmer for 4-5 minutes until thickened.

Stir in grated Parmesan cheese until melted. Season with salt, pepper, and red pepper flakes if using.

Combine the drained pasta and broccoli with the sauce, ensuring everything is coated. Add pasta water if the sauce is too thick.

Stir in lemon juice and chopped basil. Toss until combined.

Serve warm, garnished with extra Parmesan cheese and basil.