1. Make a very thick roué by heating the oil in a medium saucepan; adding the flour and cooking for a few minutes; adding the salt and taking it off the heat; adding the milk all in one go and return to the heat, stirring constantly until very thick.
2. Let the roué cool a little, then add protein and relish.
3. Adjust seasoning and let cool until cold then let rest in fridge for an hour.
4. Set up two flat bowls or plates; one with the beaten egg the other with the breadcrumbs.
5. Roué mix should be stiff enough to roll into balls or elongated balls. Then, dip each ball or croquette first into egg and then breadcrumbs. Repeat twice.
6. Shallow fry crumbed croquettes in extra olive oil.
Serve with extra relish!