Cut each slice of bread into two triangles. Top eight of the bread triangles with the mozzarella slices. Place the basil leaves and olives on top and season with salt and pepper to taste. Lay the other eight triangles of bread over the top and press down around the edges to seal.

Mix the eggs and milk and pour into an ovenproof dish. Add the sandwiches and leave to soak for 5 minutes.

Heat the oil in a large pan until a cube of bread browns in 30 seconds — the oil will then be hot enough for deep-frying. Before cooking the sandwiches, squeeze the edges together again.

Carefully place the sandwiches in the oil and deep-fry for 2 minutes or until golden, turning once. Remove the sandwiches with a slotted spoon and drain on absorbent paper towels. Serve immediately while still hot.