Soak the dried mushrooms in a heatproof bowl just covered with the boiling water for 15 minutes. Meanwhile, heat the butter and oil in a frying pan, add the onion and fry gently for 10 minutes until softened and just beginning to brown.
Tip the chicken livers into a sieve, rinse with cold water, drain well, then roughly chop, discarding any white cores. Add to the onions with the garlic and fry for 4–5 minutes, stirring until browned.
Add the mushrooms and their soaking liquid, the thyme leaves, red wine and some seasoning. Cover and cook for 5 minutes, then cool slightly.
Purée the liver mixture in a food processor or liquidizer until smooth. Spoon into four small dishes and level the surface.
Sprinkle the raw onion and thyme leaves over the pâté. Melt the butter in a small saucepan, tilt the pan and scoop the clear melted butter on to the pâté, discarding the cloudy white milk solids in the bottom of the pan. Cover and chill for 3–4 hours or overnight until firm. Serve with toast and rocket leaves.