Melt butter in a small saucepan.

Transfer a few tablespoon of the butter to a frying pan and cook onion over a low heat for about 8 minutes or until onion is soft but not browned.

Increase heat to medium, add livers and cook, stirring frequently for 5-6 minutes or until livers are no longer pink in the middle.

Remove 100g (3.5oz) melted butter from the saucepan and reserve for topping the pâté.

Place livers and onion in a food processor with the melted butter left in the saucepan. Add sherry vinegar and whizz for a few minutes until pâté is very smooth. Taste and season with salt and a little more vinegar if needed.

Pass pate mixture through a fine sieve. Divide between serving bowls.

Top with remaining melted butter and refrigerate until butter is set.