Wash the leeks and cut into fine rings. Melt the butter in a pot and gently simmer the leeks. Melt butter in another pot, add flour to the melted butter and let it dry gently. If you notice a waffle smell, add the milk and whisk away all the lumps.

Bake the redfish in hot butter. Serve the fishe together with the leek and pour a little sauce over it.