Cook the macaroni: Bring a large pot of salted water to a rolling boil. Add the macaroni and cook according to package directions until al dente — about 9 minutes. The pasta should be tender but still hold its shape when you bite into it. You’ll see the water turn slightly cloudy as the starch releases, which is exactly what you want for the dressing to cling later.

Blanch the peas: When the pasta has 2 minutes left, tip the frozen peas straight into the pot. They’ll turn a bright, vivid green within seconds. The smell of sweet peas rising with the steam is my favourite part of this step. Drain everything together in a colander and rinse briefly with cold water to stop the cooking. Shake the colander well — you want the pasta and peas as dry as possible.

Make the dressing: While the pasta cools slightly, whisk together the mayonnaise, soured cream, white wine vinegar, Dijon mustard, celery salt, smoked paprika, white pepper, and grated onion in a small bowl or a jar with a tight lid. The mixture should be pale ivory with tiny flecks of onion. Give it a sniff — it should smell tangy and savoury, not overwhelmingly vinegary.

Combine while warm: Tip the still-warm macaroni and peas into a large salad bowl. Pour about two-thirds of the dressing over the top and stir gently with a rubber spatula. The warmth will soften the cheddar and help the dressing coat every nook and cranny of the pasta. You’ll see the sauce turn from thick to silky as it warms up.

Add the cheese: Sprinkle the grated cheddar over the pasta and fold it in. The cheese will start to melt slightly from the residual heat, creating little creamy pockets throughout the salad. Don’t overmix — you want distinct strands of cheese, not a uniform paste. The texture should look marbled with orange and white.

Rest and season: Cover the bowl with cling film and let it sit at room temperature for 10 minutes. This rest is crucial — it allows the pasta to absorb the dressing. After resting, taste a forkful. The macaroni should be creamy but not soupy, with the cheese still slightly distinct. Adjust seasoning with salt and pepper if needed. Stir in the chives just before serving.

Final touch: If serving immediately, drizzle the remaining dressing over the top for extra gloss. If making ahead, fold the reserved dressing in just before serving — the pasta will have absorbed the first batch overnight.