Drain and flake salmon. Add milk to make 1 cup broth. Set aside.
Melt butter in saucepan over low heat. Add onions - cook until tender. Add flour. Stir until smooth. Cook 1 minute timing constantly. Gradually add milk and salmon broth. Cook until thick, stirring constantly. Add salt and pepper. Mix with salmon and 1/2 cup corn flakes.
Chill 30 minutes. Shape croquettes. Roll in remaining corn flakes. Bake on greased cookie sheet at 400 degrees approximately 30 minutes until brown.