Lightly oil a shallow 8-inch square dish and heat your milk in a sauce pan.

In a large saucepan, heat the olive oil and the butter over medium heat. When the butter has melted, add the roasted chicken skins and spring onions and cook on a low heat for 10 minutes until soft and translucent. Remove the chicken skins before adding the flour and using a wooden spoon, mix well. Continue to stir on a low heat for about 3 minutes for the flour to cook.

Add half of the milk and increase the heat to medium-high stirring constantly with a spoon or whisk. Bring the mixture to a boil and add the remaining milk. Cook, stirring constantly with the spoon or whisk, for about 5 minutes, or until the mixture begins to thicken. Decrease the heat to medium and cook, stirring constantly to prevent lumps from forming, for about 5 minutes, or until thickened.

Add the shredded chicken meat, season lightly with salt and pepper and stir until evenly distributed. Cook for 3 minutes longer on a low heat and then pour the contents of the pan into the prepared dish. Spread the mixture evenly. Let it cool down for 10 minutes before you cover it and refrigerate for at least 4 hours, but preferably overnight to allow the mixture to set.

Break the eggs into a bowl and beat ligthly until blended. Spread the breadcrumbs on a dinner plate. Use 2 tablespoons to shape the chicken béchamel mixture into walnut-sized croquettes. Roll each croquette in the breadcrumbs, shaking off any excess crumbs, and then dip into the beaten egg. Lift each croquette from the egg and roll it again in the breadcrumbs, coating it evenly. Lay the croquettes in a single layer on a platter. Refrigerate for 30 minutes before frying.

Pour the oil to a depth of about 2 inches into a wide, deep, heavy pot and heat over high heat. When the oil is almost smoking, slip 5 or 6 croquettes into the oil, pressing on them gently with a slotted spoon to submerge them, and fry, turning them gently, for about 2 minutes, or until they are golden on all sides. Using the slotted spoon, lift out the croquettes, holding them briefly over the pot to allow the excess oil to drain, and transfer to an ovenproof platter lined with paper towels to drain further.

Keep the croquettes warm in a low oven. Fry the rest of the croquettes in the same way, always making sure the oil is very hot before adding more croquettes. When all the croquettes are fried, arrange on a platter and serve immediately.