Tip the melted butter, lemon zest,
mackerel and spring onion into a food
processor and blend until smooth. Spoon
into a ramekin and smooth the top.
For the topping, melt the 15g butter
with the horseradish, then stir in the
parsley. Carefully spoon over the pâté
to cover it. Press some parsley leaves
on top, grind over some black pepper
and chill to set the butter. Serve the
ramekin of pâté with French bread,
butter and extra horseradish sauce.