Trim the ends off the leeks (you don't have to cut all the thicker green leaves off, just the top 2cm or so). Slice a cross 5cm deep into the top of the leeks and rinse out all the grit. Finely slice the leeks.
Put a large pan over a medium heat for 2 mins. Add 2 tbsp oil and the leeks. Season with a good pinch of salt and pepper. Cook for 10 mins, stirring now and then, till the leeks are soft and lightly browned.
While the leeks fry, halve, quarter or thickly slice the mushrooms, depending on how large they are.
Crumble the stock cubes into a large pan or bowl. Stir in 2 ltrs boiling water till the stock cubes dissolve. Set aside.
Add the mushrooms to the pan. Cook and stir for 2 mins till they're juicy. Stir in the rice. Cook and stir for 2 mins.
Add a ladleful of hot stock to the rice. Keep the heat set to medium-low and cook till the rice has absorbed the stock. Stir often, but not constantly - every few mins should do. Then keeping adding the stock and stirring till all the stock has been used up and the rice is soft and creamy
While the risotto cooks, roughly chop the herb leaves. When the risotto is ready, stir in the chopped herbs. Taste and add a little more salt or pepper if you think it needs it. Serve the risotto in warm bowls.