Cook the noodles in salted water according to package instructions.

Meanwhile, melt the butter in a large frying pan or skillet over medium high heat. Once the butter is frothy, sauté the shrimp for 3-4 minutes until they turn pink. Transfer the shrimp to a bowl and set aside.

Turn the heat down to medium and add the onions. Fry for 6-8 minutes until soft and starting to color. Add the garlic, red pepper flakes and lemon zest, and cook until the garlic is cooked and aromatic.

Add a generous splash of white wine to the pan, if using, and allow it to bubble away for a few minutes to cook off the alcohol. Add the broth and stir in the cream cheese. Keep stirring until it has melted into the sauce. Stir in the heavy cream or half & half, and season the sauce to taste with salt and cracked black pepper. Allow to simmer until it has thickened.

Drain the pasta, setting aside a little bit of cooking water. Stir the pasta into the sauce and continue to cook until the sauce has coated the pasta to the desired thickness. Add a little of the pasta cooking water if you want a thinner, glossier sauce.

Return the shrimp and their resting juices to the pan until just warmed through. Season the sauce with lemon juice to taste, and serve with chopped parsley, if desired.