• 7.5 cm (3 inch) piece jamón bone
• 1.25 litres (44 fl oz/5 cups) milk
• 2–3 bay leaves
• 175 g (6 oz) butter
• 1 brown onion, finely diced
• 165 g (5¾ oz/1⅓ cups) plain (all-purpose) flour
• 85 g (3 oz/⅔ cup) cornflour (cornstarch)
• 6 hard-boiled eggs, white part only, finely chopped
• 200 g (7 oz) jamón, finely diced
• ½ teaspoon freshly grated nutmeg
• 2 eggs, lightly beaten
• 200 g (7 oz) panko breadcrumbs
• vegetable oil, for deep-frying
• sea salt flakes, to sprinkle

Infuse the flavour of jamón into the milk by heating the jamón bone, milk and bay leaves in a saucepan over medium–high heat until the milk begins to boil. Reduce to a simmer and cook for a few minutes. Remove from the heat and steep the bone and bay leaves in the milk until the liquid has cooled to lukewarm. It must not be too warm, or the following roux will become lumpy. Remove the bone and bay leaves.

To make the roux, melt the butter over low–medium heat in a heavy-based saucepan and gently sauté the onion for about 10 minutes until translucent. Don’t allow the onion or the butter to brown.

Add the flour, a little at a time, until it has been absorbed by the butter, continuously mixing with a wooden spoon. Gradually mix in the cornflour — the roux should be smooth and silky but also a very thick paste, which resembles a lump of soft raw pastry. When the roux is made, stir in the jamón -infused milk, a little at a time, making sure that each addition of milk is completely incorporated before adding more. This will ensure smooth and creamy croquettes.

Continue to cook the mixture over low–medium heat, stirring constantly, until you obtain a thick paste, the consistency of which should be similar to thick, creamy, smooth mashed potato — this should take about 40 minutes. The flour taste should be completely cooked out. (Avoid scraping up any residual mixture from the bottom of the pan, as this may colour the sauce.) Remove from the heat and mix through the egg white, finely diced jamón, nutmeg and 1 teaspoon salt. Cool slightly, then cover and refrigerate overnight.

With floured hands, take 2 rounded tablespoons of mixture at a time and form into croquette shapes, approximately 3 cm (1¼ inches) wide and 7 cm (2¾ inches) long. Dip the croquettes in the beaten egg, allowing the excess to drip off, then roll in the breadcrumbs. Continue this process until you’ve turned all the mixture into croquettes — you should have about 28. Fill a large heavy-based saucepan one-third full of oil and heat to 180°C (350°F), or until a cube of bread dropped into the oil browns in 15 seconds. Deep-fry the croquettes in small batches for 2–3 minutes, or until golden brown. Drain on paper towel, sprinkle with sea salt flakes and serve hot.