Boil your pasta in well salted boiling water, see notes below for the perfect ratio of salt to water! Reserve a cup of water before draining.
Heat the olive oil in a large fry pan over medium - high heat. Pat the shrimp dry and season lightly with salt and pepper right before frying.
Sear for 1 minute each side until just cooked through. Set aside.
Reduce the heat to medium and in the same pan add 1 tablespoon of butter and then the garlic and red pepper flakes. Cook for 30 seconds - 1 minute.
Pour in the cream and bring to a gentle simmer, turn the heat down if you need, it should only be bubbling very gently.
Use a wooden spoon or spatula to scrape up any brown bits from cooking the shrimp.
Add the parmesan in 2 or 3 separate lots, mixing and letting it melt in between each addition.
Add ¼ cup of pasta water and let it gently simmer for 2 - 3 minutes to thicken slightly.
Add the lemon juice and mix in quickly (if you have ever had trouble with lemon juice curdling a sauce then add it at same time as pasta)
Add the cooked pasta in and toss well, let it gently bubble away in the sauce for 1 - 2 minutes to thicken. Add more pasta water if you need.
You want it to seem a bit too saucy in the pan as creamy sauces dry up so quickly off the heat.
Toss through the parsley followed by the prawns to warm through.
Serve with finely grated lemon zest and some extra parsley on top.