Fill and boil your kettle. Pop the dried porcini into a heatproof jug and pour over enough water to just cover them. Leave to soak for 5 mins, then drain the porcini and tip them back into the jug. Pour in 150ml hot water from the kettle and set the porcini aside to soak for 2-3 mins.

While the porcini soak, peel and finely chop the onion. Rinse the fresh mushrooms and tear them into bite-sized pieces.

Place a large frying pan on a medium heat and add ½ tbsp olive oil, the onion and mushrooms. Scoop the porcini out of the jug (keep the soaking water) and add them to the pan. Season with a pinch of salt and pepper. Fry for 8 mins, stirring often, till softened and lightly coloured.

Meanwhile, pour the hot water from the kettle into a large pan, topping it up if necessary. Add a pinch of salt and bring the water back to the boil. Tip in the penne and cook for 8-10 mins till the pasta is al dente (soft with a slight bite).

Peel and grate or crush the garlic. Finely chop the rosemary leaves. When the veg have fried for 8 mins, add the garlic and rosemary to the pan. Cook and stir for 2 mins. Meanwhile, drain the pasta if you haven't already, and set it to one side.

Pour the porcini water into the pan and add 4 tbsp crème fraîche. Turn the heat down to low and very gently warm through for 1-2 mins. Tip in the pasta, add a pinch of dried chilli flakes (they're hot, so use as much or as little as you prefer) and gently toss to mix.

Taste the pasta and add more salt, pepper or chilli flakes if you think it needs them. Serve the mushroom pasta in a couple of warm bowls, topped with handfuls of watercress.