Fill a large pot with water and bring to a boil. Season with salt.
Add spaghetti and cook for about 8-10 minutes or until al dente.
Reserve ½ cup water. Drain.
Place shrimp in a large bowl. Season with salt and pepper.
Heat a large frying pan with 1 tablespoon olive oil over medium-high heat.
Add shrimp (prawns) in a single layer.
Cook for 3-4 minutes each side or until opaque. Remove from the pan.
To the same pan, add remaining olive oil and butter.
When butter melts, add garlic.
Saute, stirring, for 1 minute or until fragrant.
Add red pepper (chili) flakes and sprig of parsley. Saute, stirring, for about 30 seconds.
Add shrimp (prawns). Stir to combine.
Pour reserved pasta water. Season with salt and pepper.
Simmer the sauce and let it emulsify.
Add cooked spaghetti. Toss.
Add chopped parsley. Toss.
Garnish with freshly grated parmesan, if you like.