"Corned beef hash...probably has its origins in being a palatable combination of leftovers"
-The Encyclopedia of North American Eating and Drinking Traditions
Following the advice in the preceeding writeups and obtaining corned beef hash in a can, or using ready-prepared hash browns, somewhat misses the point of this simple but effective meal. Both the Webster definitions of hash come into play here- as "a new mixture of old matter; a second preparation or exhibition", cobbling together a hash should save on waste of existing ingredients (particularly potatoes), rather than requiring the purchase of new ones. This leads to a number of variations on the basic theme, and makes it a quick, cheap meal for students.
A Basic Corned Beef Hash
Ingredients (for 2)
If like me you're cooking for one, then I recommend a 200g/7oz tin of corned beef (since, usually, this is the smallest size available), a couple of small potatoes, and half an onion - they don't exactly break the bank if you can't find a use for the other half.
Preparation
Peel and cube the potatoes, transfer to boiling water and simmer for 10-15 minutes, until tender. shaogo suggests that including a bay leaf or two in the boiling water "gives a heavenly, savory flavor to the whole thing". Meanwhile, cut the corned beef and onion into small, roughly cube shaped pieces. Drain the potatoes well and cut into yet smaller, similar sized pieces. Heat the oil in a frying pan then chuck in everything. Fry for about 10 minutes over a medium heat, using a fork to mash the components together and turning half way- a hash brown-like crust should develop during cooking. Transfer to a plate and eat!
Variants
There are various seasoning options that I avoid, but you may wish to experiment with- Worcestershire or Tabasco sauce being typical. For a more complete meal, the addition of baked beans is common: you can either prepare them separately and mix on the plate, or save on washing up by simply chucking them into the frying pan too. Use about half a tin of beans per person. asofel suggests peas above; Americans seem to consider corned beef and cabbage a traditional Irish combination, but if it is then it seems the English never caught on.
If you have more time and cooking facilities, or just can't get the potatoes to hash correctly, you could instead try an oven baked version. Prepare the potatoes as mash instead, whilst frying the corned beef, onions and beans together as usual. Transfer the fried ingredients to an oven dish, top with the mash, top that with some butter, then give it about 20 minutes on gas mark 7. Lou advises that oop north, this is generally how it is prepared, but by constructing the hash in layers in a casserole dish, rather than premixing. Thus start with corned beef and onion, then a layer of beans, then sliced potatoes, brushed with oil or butter.
References
The Food timeline.
Hard up and hungry- a cook book of hassle free recipes and guide to civilised survival for students.
Much personal experience, this being one of the few meals I can eat that requires something resembling cookery!