Cut the fish fillets in half and put them in a tray. Pour the milk over them and cover with foil. Leave them for 1 hour in the fridge to marinate.
Stir this mixture and roll the fillets in it on both sides. Shake off the excess, heat the oil and fry the fillets for a few min. until golden. Take them out and drain onto paper towels.
Make the garnish by boiling the potatoes, cutting them, adding the onions and seasoning with salt, black pepper, olive oil and vinegar to taste.
You can use any other garnish of your choice. The breading is suitable for every kind of white fish.