Tuna with Oloroso

This is a version of ‘atún encebollado’ (tuna with sweet onions), a recipe given to us by Miguel Valdespino of the famous Valdespino sherry bodega in Jerez. The tuna caught off the Atlantic coast of southern Spain is among the best in the world and huge slabs of it, sometimes whole fish, appear in the local fish markets of Jerez and Cádiz during the season. Look out for deep red/purple shiny, firm flesh and do not compromise with the often grey, dull, flabby cuts that certain supermarkets d