1 lb Smoked cod

    1/2 lb Onions

    1/2 lb Shelled peas

     10 fl Milk *

      1 oz Flour

      1 t  Dry mustard

      1 oz Butter

      2 lb Mashed potato

  * (or substitute 5 oz milk and 5 oz cream)
  .
  Chop onions roughly and fry in butter until tender.  Remove from heat an
  stir in flour and mustard.  Add milk.  Return to heat and stir until
  thickened.  Add cod, cut into 1/2-inch cubes, and peas. Turn into
  ovenproof dish and cover with mashed potatoes.  Bake in a moderate oven at
  400F/200C, for 35-45 minutes, or until golden brown.

  .
  (Though not traditional, the addition of 2-3 oz of cheddar cheese to the
  sauce makes this an extremely tasty dish.)