Pour the stock, wine and rosemary into a shallow saucepan, bring to the boil and simmer until it’s reduced to half the original quantity. Add the mushrooms and simmer for a further 2-3 minutes.
Loosely roll up the fillets of fish and put on top of the mushrooms. Cover with a lid and gently poach the fish for around 5-8 minutes, or until it’s cooked through.
Put the spinach in a colander then pour over a kettleful of boiling water. Drain well then divide between four warm plates. Remove the plaice from the stock and mushroom mixture and put on top of the spinach.
Add the yogurt to the stock and mushrooms and gently heat through (don’t allow it to boil or it may curdle) and pour over the fish. Serve with the potatoes, asparagus and green beans.