For the tuna croquettes, drain and shred the tuna. In hot oil, toast the flour until light yellow. Slowly pour in the milk until you have a thick sauce.
Stir in the tuna and season vigorously with salt and pepper. Let stand for at least 6 hours (better until the next day).
Using 2 spoons, cut croquettes from the dough and roll into small sticks. Dredge in flour, beaten egg and then in breadcrumbs. Fry the tuna croquettes in plenty of fat until golden brown and serve hot.