Cook the pasta in salted boiling water according to package directions.
Heat 1 tablespoon of butter in a large pan over medium high heat.
Add the shrimp to the pan and season with salt and pepper.
Cook the shrimp for 3-4 minutes, stirring occasionally, until shrimp are pink and opaque.
Add the garlic to the pan and cook for an additional 30 seconds.
Remove the shrimp from the pan and cover to keep warm. Wipe out the pan with a paper towel.
Melt 4 tablespoons of butter in the pan over medium heat.
Add the heavy cream and simmer for 4-5 minutes or until just thickened - do not let it boil.
Whisk in the parmesan cheese, stirring continuously, until the cheese has melted.
Remove the sauce from the heat, then stir in the lemon juice.
Season the sauce with salt and pepper to taste.
Drain the pasta and place it in the pan with the sauce. Add half the shrimp and toss everything together to combine.
Arrange the other half of the shrimp on top of the pasta. Sprinkle with parsley. Garnish with parsley sprigs and lemon slices if desired, then serve.