Boil the pasta: Bring a large pot of generously salted water to a rolling boil. Add the pasta shells and cook according to package instructions until al dente — usually 8–9 minutes. The shells should feel firm at the centre when you bite one. Before draining, scoop out 200ml of the starchy pasta water and set it aside. Drain the shells in a colander but do not rinse them; you want that starch to help the sauce cling.

Start the sauce: While the pasta boils, place a large frying pan or skillet over medium heat. Add the butter and let it melt slowly, tilting the pan to coat the surface. The butter will foam gently at first, then settle into a quiet, golden liquid. When the foam subsides, add the minced garlic and stir continuously for about 45 seconds — you’ll smell a fragrant, nutty aroma, and the garlic should turn pale gold, not brown.

Add the lemon and cream: Sprinkle in the lemon zest and pour in the lemon juice. Stir once, then immediately pour in the double cream. The mixture will bubble softly at the edges. Whisk or stir gently for 1–2 minutes until the sauce thickens slightly and turns a uniform, pale yellow colour. You’ll see it coat the back of a spoon.

Incorporate the peas: Tip the frozen peas directly into the sauce. Stir them through and let them cook for 2 minutes. The peas will turn a bright, vivid green and soften just slightly, releasing a sweet, grassy scent. They do not need to be fully thawed before adding — the heat of the sauce will do the work.

Combine pasta and sauce: Add the drained pasta shells to the pan with the sauce. Sprinkle over the grated Parmesan, salt, and black pepper. Toss everything gently with a wooden spoon or spatula for about 1 minute, allowing the cheese to melt into the cream. The sauce should look glossy and cling to each shell. If it seems too thick, add a splash of the reserved pasta water — about 2 tablespoons at a time — until it reaches a silky, flowing consistency.

Finish and rest: Remove the pan from the heat. Let the pasta rest for 1 minute — this allows the sauce to settle and the flavours to meld. The shells will absorb a little of the creamy liquid, becoming plump and tender. Taste and adjust salt or lemon juice if needed.

Serve immediately: Divide the pasta among warm bowls. Scatter fresh parsley on top if using, and add an extra grating of Parmesan or a twist of black pepper at the table. The dish is best eaten straight away, while the sauce is still luscious and warm.