Brown the chicken. Pat the chicken thighs dry with kitchen paper — this is crucial for a good sear. Heat the olive oil in a large, deep skillet or Dutch oven over a medium-high flame. Once the oil shimmers and you see the faintest wisp of smoke, lay the chicken thighs in, skin-side down if they have skin, or just one flat side. Let them cook undisturbed for 5-6 minutes. You'll hear a steady, satisfying sizzle, and the underside should turn a deep, burnished gold with crisp edges. Flip and cook for another 4 minutes. The chicken should feel firm to the touch but not stiff. Lift it onto a plate and set aside.

Sweat the aromatics. Reduce the heat to medium. Add the butter to the same pot. As it melts and foams, scrape up any browned bits from the bottom with a wooden spoon — that's pure flavour. Add the chopped onion and stir. Cook for 4-5 minutes, until the onion turns translucent and softens, releasing a sweet, mellow scent. The sizzle will quieten as the onion releases its moisture.

Bloom the garlic and herbs. Tip in the minced garlic, dried thyme, and dried rosemary. Stir constantly for about 45 seconds. The smell will shift from sweet onion to pungent, fragrant garlic — be careful not to let it brown, as burnt garlic turns bitter. You want it just fragrant and softening.

Toast the pasta. Pour the dried shells into the pot and stir them through the garlic butter for 1-2 minutes. You'll hear the shells clatter and click against the metal, and they'll take on a slightly glossy, warm look. This toasting step adds a subtle nuttiness to the final dish.

Add the liquid. Pour in the hot chicken stock and the double cream. Stir gently to combine, scraping the bottom again to release any last bits of flavour. The liquid will look pale and thin at first, but don't worry. Season with the salt and black pepper. Bring the mixture to a gentle simmer — you want small, lazy bubbles breaking the surface, not a rolling boil.

Return the chicken and simmer. Nestle the browned chicken thighs back into the pot, pushing them down so they're mostly submerged. Reduce the heat to low, cover with a lid, and let it cook for 18-20 minutes. After about 15 minutes, lift the lid and give it a gentle stir. The pasta should be tender but still with a slight bite, and the sauce will have thickened noticeably, clinging to the shells like a warm blanket. The colour will have deepened to a pale gold, flecked with herbs.

Finish with cheese and peas. Remove the pot from the heat. Lift out the chicken thighs and set them on a board. Stir in the frozen peas (if using) and the grated Parmesan. Stir vigorously for about 30 seconds — the residual heat will melt the cheese into the sauce, turning it glossy and thick. You'll see the sauce change from thin to velvety right before your eyes. Shred or chop the chicken into bite-sized pieces, then stir it back into the pot. Taste and adjust seasoning with a pinch more salt or a crack of pepper.

Rest and serve. Let the pot sit, lid off, for 3-4 minutes. This resting time allows the sauce to settle and the flavours to marry. Sprinkle with fresh parsley just before serving. The final dish should look creamy, with the shells glistening and the chicken scattered throughout.