Peel and finely dice the onion. Heat 1 tbsp olive oil in a large pan over a medium heat. Add the onion and cook for 8 mins, stirring, till starting to soften.

While the onion cooks, pour 700ml boiling water into a heatproof jug. Crumble in the stock cube and add the dried porcini. Stir to dissolve the stock cube then set aside to soak for 10 mins.

Meanwhile, peel and slice 1 of the garlic cloves. Slice the portobello mushrooms.

Add the garlic to the onion and cook for a further 1 min. Add the portobello mushrooms to the pan. Scoop the porcini mushrooms out of the stock with a slotted spoon or tongs and add them to the pan. Cook, stirring often, for 3 mins till the mushrooms are just starting to soften.

Pour in the risotto rice and stir to coat in the oil. Turn the heat down a little to medium-low. Add a splash of the stock – around 100ml. Cook, stirring often, till the stock has been absorbed. This should take 2-3 mins. Add another splash of stock and carry on cooking the rice and veg. Do this till you have added all but the last 100ml of the stock. This should take around 20 mins.

While the risotto is cooking, strip the leaves from the tarragon sprigs and finely chop them. Zest and juice the lemon. Peel and finely chop the remaining garlic clove. Place everything in a small bowl, add 1 tbsp olive oil and a pinch of salt and pepper. Stir to mix. This is your gremolata.

Stir the last splash of stock into the risotto and cook, stirring, for 2 more mins. Taste and add a little more salt or pepper if you think it needs it (remember the gremolata has plenty of flavour to add to the risotto too).

Spoon the risotto onto warm plates and add a few handfuls of the lamb's lettuce. Spoon over the tarragon gremolata and serve.