Bring a large pot of salted water to a boil and cook 10 ounces penne according to package directions until al dente, then reserve a small cup of pasta water and drain.
While the pasta cooks, melt 2 tablespoons butter in a large skillet over medium-high heat.
Whisk in 1½ teaspoons flour and cook for about 1 minute to remove the raw flour taste.
Add the 3 cloves minced garlic and 1/3 cup chicken broth, whisking for about 1 minute until combined and slightly thickened.
Pour in 1 cup heavy whipping cream and continue whisking for a few minutes until the sauce coats the back of a spoon but is not gummy; reduce heat if needed.
Stir in 1/2 teaspoon Italian seasoning, 1/2 teaspoon salt, 1/4 teaspoon pepper, and 1/2 cup freshly grated Parmesan until the cheese melts, then remove the skillet from the heat.
Add the drained penne to the sauce and toss to coat, adding a splash of reserved pasta water if needed to loosen the sauce; serve immediately.