Preheat the oven to 160°C fan/350°F/Gas 4.

Place the onion, garlic, harissa, smoked paprika, ground cumin and coriander, olive oil and coriander stems in a food processor, along with 11/2 teaspoons of salt and a good grind of black pepper. Blitz well to combine and then pour this into a medium roasting tray or ovenproof dish, about 30 x 22cm (12 x 81/2in).

Add all the mushrooms and mix to coat. Cover with foil and bake for 50 minutes, stirring halfway through, until the mushrooms are really soft.

Add the spinach and all but 1 tablespoon of the coriander leaves, stir, then re-cover and bake for another 10 minutes, to allow the spinach to wilt. Remove the foil, give everything a stir, increase the oven temperature to 180°C fan/400°F/Gas 6 and bake, uncovered, for a final 15 minutes, to allow the sauce to reduce a little and thicken up.

While the mushrooms are cooking, place all the ingredients for the butter bean mash in a food processor along with 1/2 teaspoon of salt. Blitz well until smooth (you might need to add a couple more tablespoons of bean stock from the butter bean jar or water to get your desired consistency), then set aside. When the mushrooms are almost ready, warm the mash up in a saucepan over a low heat.

To serve, divide the mash between two or four plates and make a little well in the middle of each portion. Spoon in the mushrooms, then finish with the final sprinkling of coriander leaves.