Soften whole dried mushrooms in hot water for at least 20 minutes before adding to the soup.
(You can use the flavorful soaking liquid as part of the recipe’s cooking liquid)
In a large saucepan put the olive oil and fry the bacon.
Add the butter, the finely chopped red onion and leek, and let soften over a low flame, stirring until lightly browned.
Add finely chopped carrots and celery, cubed squash and porcini mushrooms.
Add two ladles of broth and simmer for about 15 minutes.
Finally add the barley, the tomato paste and the remaining vegetable broth, season with salt and cook for about 20-25 minutes.
I chose a quick-cooking barley, ready in 10 minutes, but for my personal taste, in soups I prefer to let it cook for 15 minutes longer, because I like the more fleshy grains.