Rinse the barley under cold water. Tip into a pan and cover with 500ml boiling water. Add a pinch of salt and simmer with the lid on for 30 mins.
Crumble the stock cube into a heatproof measuring jug. Tip in the dried porcini mushrooms. Pour in 400ml boiling water and leave to infuse.
Peel and finely slice the onion. Finely slice the leek. Thickly slice the mushrooms leaving any smaller ones whole.
Heat a large pan over a medium heat. Add 1 tbsp oil to the warmed pan. Add in the diced chicken leg and cook on a high heat for 5 mins till golden. Lift the chicken into a bowl using a slotted spoon.
Add the onion, leeks and mushrooms to the pan. Cook for 3 mins till just softened and juicy. Tip the chicken back in, along with any juices. Pour in the porcini and chicken stock. Simmer for 15 mins to cook the chicken through.
When the barley is nearly cooked, pour the cream into the mushroomy chicken. Simmer over a low heat for 5 mins. Add most of the thyme leaves (save a few for later).
Tip the spinach into the barley pan. Stir till wilted.
Season the barley and chicken. Serve in warm bowls with the remaining thyme leaves scattered over.