Wash the cockles well and leave them in salt water for a few hours to release any grit.
Place the cockles in a cooking pot together with the white wine. Cover and cook over a medium heat until the cockles open. Then strain the broth and take the cockles off their shells. Reserve.
Chop the garlic and cook it for a minute in a hot frying pan with a bit of olive oil. Add the flour and cook it for another minute.
Pour the cockles broth into the pan and reduce it for a few minutes over a medium heat until the consistency of the sauce gets thicker. Add the cockles into the pan, bring to boil and take the pan off the heat. Keep warm.
Season the hake medallions and oil them on both sides. Cook them in a pan for three minutes on each side.
Place the hake medallions on a serving plate, spread some finely chopped spring onion over and cover with the cockles sauce before serving.