In a large pot, add the butter, onion, and garlic. Cook over medium heat until the onions start to soften and become translucent.

Add the shrimp, spaghetti, and 2 cups of water to the same pot. Cover and cook until the pasta is al dente.

Pour in the cream and parmesan cheese. Stir until the cream is absorbed and it creates a smooth sauce.

Remove from heat, garnish with some parsley if desired, and serve.