Sauté the aromatics: Heat the olive oil in a large frying pan or skillet over medium heat. Add the diced onion and cook for 3–4 minutes until it becomes translucent and you can smell its sweet, savoury aroma. Add the minced garlic and cook for another 30 seconds until fragrant, but not browned.

Cook the mushrooms: Tip the sliced mushrooms into the pan. Spread them out in a single layer and let them cook undisturbed for 2 minutes. You'll hear a gentle sizzle as the moisture releases. Stir and continue cooking for another 3–4 minutes until the mushrooms are golden brown on the edges and have released their liquid, which should have mostly evaporated. The pan should look dry again.

Wilt the spinach: Add the fresh spinach to the pan in handfuls. Stir it through the hot mushrooms, and watch as the leaves turn bright green and collapse into a soft, silky mass. This takes about 1–2 minutes. Once all the spinach is wilted, remove the pan from the heat temporarily.

Build the creamy sauce: Return the pan to a low heat. Add the double cream, softened cream cheese, grated cheddar, and Parmesan. Stir continuously with a wooden spoon or spatula. As the cream cheese melts, the sauce will turn from a pale white to a rich, golden-yellow colour. The texture should become thick and velvety, coating the back of your spoon. Stir in the dried thyme, salt, and black pepper.

Cook the pasta directly in the sauce: Add the uncooked rotini to the pan along with the vegetable stock. Stir everything together to coat the pasta. Bring the mixture to a gentle simmer — you'll see small bubbles breaking the surface. Reduce the heat to low, cover the pan with a lid, and let it cook for 12–14 minutes. Stir once halfway through to prevent the pasta from sticking to the bottom.

Check for doneness: After 12 minutes, test a piece of rotini. It should be tender but still have a slight bite (al dente). If it's still too firm, add an extra splash of stock or water and cook for another 2 minutes. The sauce should have thickened and become glossy, clinging to each spiral of pasta. If it looks too thick, stir in a little more stock to loosen it.

Rest and serve: Remove the pan from the heat and let it sit, covered, for 2–3 minutes. This resting time allows the sauce to settle and the flavours to meld together. The pasta will absorb a bit more liquid, making every bite perfectly creamy. Serve immediately while hot.