The meals we serve for our most festive occasions - the turkey at Thanksgiving, the steak on the Fourth, the ham at Easter - are so simple to prepare, so unchallenging, that many cooks would just as soon sit out a holiday season.

Nothing is easier than cooking a non-holiday ham. Oh, I suppose you could not but an uncooked ham and cut away the mold and scrub it with baking soda and allow it to soak in a bathtub for a fewdays - but there's no reason not to buy a smoked or ready-to-eat ham. All you do then if heat it up, smear on the sauce, heat it some more and cut in very thin slices.

Since today's meal is built around such a simple theme, we'll make the rest of it a little more complicated. The five-day spinach, for example, refers not to the fact that the spinach ripens in five days or it can be eaten over five days, but that it takes five days to cook. That's not so bad. To make a proper Potatoes Anna can take a lifetime.

The Staples: Make sure these are all on hand: salt, pepper, mustard, beer, rum, whole cloves.

The Shopping List: 1 ham (12 to 14 pounds, precooked or smoked); 3 pounds potatoes; 2 pound fresh spinach (very fresh if possible); 5 large bananas; 1 lemon; brown sugar.

Prepare in Advance: The spinach. Today's recipe for spinach was discovered by the famed food writer Brillat-Savarin, who extracted it from a village priest famous for his spinach. Since I have known only one person who followed this recipe to the letter, I will offer a shorter version as well. (Significantly enough, the one person who went to the trouble re ceived such compliments that she now serves it at every dinner party.)

The First Day: Rinse the fresh spinach carefully, removing all traces of sand. Using a small casserole pot, melt 1 stick of butter over low heat. Add the rinse spinach and cook slowly for 1/2 hour, allowing the butter and spinach to blend together. Turn off heat, allow pot to cool and put in refrigerator.

The Second Day: Put the pan back over a very low heat, add 1/2 stick of butter to spinach and cook for 15 minutes, remove from heat and refrigerate.

The Third Day: Repeat second day instructions. According to Brillat-Savarin you must be careful here: "There will be an exceedingly tempting aroma. Do not be tempted."

The Fourth Day: Repeat the second day process again. (The spinach will be giving an irresistible aroma. Resist.")

The Fifth Day: For the last time repeat the process and cook it over low heat until the butter is fully absorbed by the spinach. And today you don't resist.

A shortcut: Cook the spinach in butter in for 10 to 12 minutes or until tender.

3:30 P.M. (or earlier, for a smoked ham): Allow about 15 minutes a pound for heating up a ready-to-eat ham, about 25 minutes a pound for a smoked ham. Set the oven temperature for 325 degrees. Put in the ham. That's it, for a while.

5 P.M.: The potatoes Anna. Peel the potatoes and slice them very thin. Put inside a bowl of ice water. Butter the inside of a medium-sized casserole pot and add a couple of layers of the sliced potatoes. Add dots of butter - perhaps 1/4 stick - over the layer of potatoes and a scattering of salt and freshly ground pepper. Now add more potatoes. After every few layers of potatoes, add butter, salt and pepper. And so on until the potatoes are all in the casserole. Some also add grated onions and parmesan cheese, but that can wait for another time.

If you have a second oven, you'll cook the potatoes at 400 degrees for approximately an hour. If not, you'll have to cook them in an oven with the ham and allow at least an hour and 15 minutes, probably longer. The potatoes are done when they're brown and crisp on the outside and steaming hot on the inside.

The proper way to serve Potatoes Anna is to turn the pot upside down, forming a brown-surfaced mound of potatoes. (Danger! This first time, let's just spoon it directly from the casserole.)

5:45 P.M. Oh, yes the ham. Remove ham from the oven. If the ham has a rind, cut away the skin and much of the fat.Using a sharp knife, criss-cross the surface of the ham, with lines. Insert whole cloves - three dozens of them - at the intersectionof the cut times.

Now mix together one cup of brown sugar and 3 to 4 tablespoons f mustard. Add just enough of the beer to make this a paste. Smear the paste over the surface of the ham and return it to the oven. Repeat this two or three more times during the baking time.

6:30 P.M.: The ham , the potatoes and the spinach should all be done and poping hot. As you remove the food from the oven, turn heat up to 425 degrees.

Put 1/2 stick butter in a heatproof dish and melt in oven. (Incidentally, it strikes to me that this is no a meal for anyone trying to cut down on butter.) Slice the bananas thickly. When butter is melted, add sliced bananas and let stand on counter. Twelve minutes before the end od dinner, interrupt your repast to sprinkle dessert with the juice of one lemon and a dusting of brown sugar and return to oven for 3 or 4 minutes. Finally, add 1/3 cup of rum, strike a match and serve it alight.