Mix dried mushrooms with boiling water in a bowl and leave to soak for 10-15 minutes until soft. Squeeze mushrooms to remove excess liquid and reserve the liquid (it’s like a mushroom stock with tons of flavour). Finely chop the soaked mushrooms and set aside.
Heat olive oil in a saucepan and add barley, lightly frying until barley is toasted (about 2 minutes). Add onion or shallots and garlic and sauté until soft (about 5 minutes).
Add wine and let it bubble for a couple of minutes, then add the stock and 1 cup of the reserved mushroom liquid. Cover partially with a lid and simmer for 45-50 minutes until barley is tender (it will still have a bit of bite to it) and the liquid is mostly absorbed. Stir a few times during cooking. Turn off heat but leave the lid completely on to allow the barley to keep steaming.
Heat 50g butter in a large frying pan, add mushrooms (both dried and fresh) and sauté for 5-6 minutes until soft and golden. If the mushrooms are looking dry in the pan at any time, add a bit of stock to help sauté them.
Stir spinach, parmesan and half the cooked mushrooms through the barlotto. Some people like to stir in another knob of butter at this point for extra richness. Season to taste with salt (or a little soy sauce for more depth of flavour) and freshly ground black pepper.
Heat knob butter in a frying pan until starting to brown then add sage leaves and cook for 1-2 minutes until crispy.
Divide barlotto between plates. Garnish with rest of mushrooms, extra grated or shaved parmesan and fried sage leaves.