Remove the skin and bones from the mackerel.

Place the mackerel, butter and creme fraiche into a food processor, process until smooth.

Add the lemon zest and juice, parsley, Worcestershire sauce and salt and pepper to taste. Mix well. Stir in the mushrooms and place mixture into a serving dish. Chill well.

Alternatively serve in ramekins and top with melted butter. Garnish with lemon and parsley.