Bring a large pot of salted water to a rolling boil and cook the penne pasta according to package directions until al dente. Reserve 1 cup of pasta water before draining.

Heat olive oil and butter in a large skillet over medium heat until butter melts and begins to foam slightly.

Add minced garlic and sauté for 60-90 seconds, stirring constantly, until fragrant but not browned.

Sprinkle flour over garlic mixture and whisk continuously for 1-2 minutes to create a roux.

Slowly pour in vegetable broth while whisking constantly, then add heavy cream and whisk until smooth.

Bring sauce to a gentle simmer and cook for 3-4 minutes, stirring occasionally, until thickened.

Add fresh spinach in batches, stirring after each addition until all spinach is wilted.

Stir in Parmesan cheese, Italian seasoning, salt, black pepper, and red pepper flakes if using. Mix until cheese melts.

Add drained pasta to skillet and toss together, adding reserved pasta water as needed to reach desired consistency.

Remove from heat, squeeze lemon juice over pasta, and toss once more.

Serve immediately topped with additional Parmesan and black pepper.