Cook the spaghetti according to package directions until al dente.
Reserve 1 cup of pasta water, then drain spaghetti.
In a large skillet, melt the butter over medium heat.
Add the heavy cream to the melted butter, stirring constantly.
Gradually whisk in the grated Parmesan cheese until melted and smooth.
Season with salt and freshly cracked black pepper to taste.
Add the drained spaghetti to the sauce, tossing to combine.
Serve immediately, garnished with fresh parsley.