When I think of all the goulashes, watery soups and greasy mixtures being passed off as Irish lamb stew, I wonder why I continue to order it in restaurants. The answer, I suppose, is that genuine Irish lamb stew is wonderful, and I keep trying to relive the experience.

But what is genuine Irish lamb stew?

After looking vainly through several early 19th-century Irish cookbooks, I remembered Alexis Soyer. He was the famous chef of the Reform Club in London who went to Ireland during the Potato Famine of 1845 and set up soup kitchens, where hundreds of thousands ate inexpensive but nourishing sourps prepared under his direction. In an 1855 edition of Soyer's "A Shilling Cookery for the People," I found a long, elaborate and excellent discussion of Irish stew.

From Soyer on, many Irish, English, Scottish and even several American cookbooks regularly offer recipes for Irish stew, all basically the same. The ingredients are lamb, potatoes and onions; the spices are salt, pepper, perhaps a touch of parsley or bay leaf, but noting else.

The following recipe is as close as possible to the older, more authentic recipes, skipping frivolous modern-day additions such as paprika, carrots, thyme and other "foreign elements.

Once you spend the initial 20 to 30 minutes on preparation, you don't have to do anything else.

IRISH LAMB STEW

(8 servings) 2 pounds boneless cubes of lamb, free of fat and gristle (reserve bones for making broth) 5 cups water 2 teaspoons salt 1 tablespoon shortening 2 pounds red potatoes 1 1/2 pounds onions 1/2 teaspoon coarsely ground black pepper 1 bay leaf (optional) 1 tablespoon chopped green parsley (optional)

Select a heavy cast-iron or other metal pot or oven-proof casserole with a tight-fitting lid. (A 3-quart dutch oven is suitable.)

Put bones and fat from lamb in a separate pot with 5 cups water and 1 teaspoon salt. Bring to a boil, skim off fat and simmer.

Brush bottom of heavy stew pot with 1 tablespoon shortening. Peel potatoes. Leave 8 largest ones whole, and slice others 1/4 inch thick, halving large onions before slicing.

Line bottom of stew pot with sliced potatoes. Distribute half the onions evenly over potatoes. Dredge lamb cubes with 1 teaspoon salt and black pepper, and distribute meat over onions. Top with remaining onions and 8 whole potatoes. Add bay leaf.

Pour 2 1/2 to 3 cups of broth from bones into stew pot. Cover and place in a preheated 350-degree oven. Bake 2 hours. Continue to simmer remaining broth.

After 2 hours, strain remaining broth and pour into stew pot. Cover and back another 30 to 45 minutes. Remove from oven, sprinkle with chopped parsley, and serve at once.

If you buy your lamb already boned and cubed, so that you have no bones with which to make broth, substitute an 11-ounce can of chicken broth, diluted, plus 2 1/2 cups water. Simmer this mixture and add it where the broth is called for. Omit the teaspoon of salt used in the broth.

Be sure to have salt and, preferably, a pepper mill on the table. The onions and sliced potatoes will cook into a soft substance which you can ladle.

My first choice with this Irish stew is a good imported Irish beer, either at room temperature, as they drink it in Ireland, or chilled, which is more to American taste. You also can mix it with that thich, bittersweet, malty miracle called Guinness Stout. Guinness, if drunk by itself, tastes awful to most Americans, but mixed to the proportions of two-thirds beer and one-third Guinness, it seems to please them.