Heat the olive oil in a large pot over medium heat. Add the onion; cook and stir until onions are limp, but not brown, about 5 minutes. Mix in the celery and carrot; cook for another 5 minutes. Stir in the barley and lentils so they are coated with oil, continue to cook and stir until lightly toasted.
Pour in the beef stock and season with thyme, parsley, pepper and the bay leaf. Bring to the boil. Add the porcini mushrooms, cover and simmer for 25 minutes over low heat. Add the button mushroom, cover and continue cooking for another 30 minutes, stirring occasionally. Mix in sherry during the last 5 minutes. Taste and adjust seasoning if needed before serving.