Bring a large pot of salted water to a boil over high heat. Cook the penne until it is al dente (about 2-3 minutes less than the cooking time listed on package directions).
As the pasta cooks, melt the butter in a large 12-inch skillet set over medium heat. Sprinkle the melted butter with the flour and use a whisk to combine (it will form a thick paste). Cook the paste (roux) for about 1 minute, stirring often.
Add the minced garlic followed immediately by the vegetable or chicken broth (you may also use your favorite dry white wine) and lemon juice. Whisk continuously as it comes to a gentle simmer. Allow it to simmer/bubble for about 30 seconds.
Still whisking, slowly stir in the cream until fully combined with the flour mixture. Bring to a gentle simmer then reduce heat to medium-low. Cook over medium-low heat for about 2 minutes, or until it has thickened slightly.
Stir in the grated parmesan cheese and season with salt and pepper, to taste. Remove from heat.
Reserve at least 1 cup of hot pasta water before draining the pasta. Add the drained pasta to the sauce and toss to coat. Add some of the reserved pasta water to the skillet, as needed, if the sauce becomes too thick (the starch from the pasta will help thicken the sauce).
Season with additional salt and pepper, to taste, and serve garnished with additional grated parmesan cheese and fresh parsley, if desired.