Bring a large pot of generously salted water to a rolling boil. The water should taste as salty as the sea — this is your only chance to season the pasta itself. Drop the spaghetti in and cook it for one minute less than the packet suggests. You want it al dente, with a tiny white core still visible when you bite a strand. Reserve about 250ml of the starchy pasta water before draining. The starch is liquid gold for your sauce.

While the pasta cooks, pat the prawns completely dry with kitchen paper. Any moisture on the surface will steam them rather than sear them. Season them lightly with salt and a pinch of black pepper. Heat the olive oil in a large frying pan over a medium-high flame until it shimmers and ripples. Lay the prawns in a single layer — you should hear an immediate, satisfying sizzle. Cook for 90 seconds on the first side until the edges turn a deep coral pink and the flesh begins to curl slightly. Flip and cook for another 45 seconds. The prawns should be just cooked through, with a tender, springy bite. Transfer them to a plate and set aside.

Reduce the heat to medium-low and add the butter to the same pan. Watch it melt slowly, turning from solid to a foamy, nutty-scented liquid. Scrape up any browned bits from the bottom of the pan with a wooden spoon — those little caramelised pieces are pure flavour. Add the minced garlic and red pepper flakes, if using. Stir constantly for about 45 seconds until the garlic becomes fragrant and softens, but do not let it brown; you want it pale gold and sweet, not bitter.

Pour in the chicken stock and let it bubble gently for 2 minutes, reducing slightly. The liquid will take on a pale, translucent appearance and smell deeply savoury. Now add the double cream in a slow, steady stream while stirring. The sauce will lighten in colour and start to thicken around the edges of the pan. Let it simmer gently for another 2 minutes, until it coats the back of a spoon and leaves a clear trail when you draw a finger through it.

Stir in the grated Parmesan cheese, lemon juice, and lemon zest. The cheese will melt into the sauce, making it even thicker and glossier. Taste it now — you should notice a bright, acidic lift from the lemon that balances the richness. Season with salt and pepper. If the sauce seems too thick, add a splash of the reserved pasta water; it will loosen it and help it cling to the spaghetti later.

Add the drained spaghetti directly to the pan with the sauce. Use tongs or a pasta fork to toss and turn the pasta, coating every strand in that velvety cream sauce. You’ll see the sauce tighten and become more cohesive as it mixes with the starch from the pasta water. If it looks dry, add another splash of reserved water. Cook everything together over low heat for 1 minute, allowing the pasta to absorb some of the sauce.

Return the cooked prawns to the pan, along with any juices that have collected on the plate. Toss gently — you want to warm the prawns through without breaking them apart. Sprinkle over the chopped parsley and give it one final gentle turn. The prawns should glisten against the creamy, golden strands of spaghetti.