No matter how you spell it - ''filo,'' ''fillo,'' or ''phyllo'' - those tissue-thin sheets of strudel dough are compatible with meat, fish, cheese, vegetables, fruit, and nuts. Phyllo can be baked, fried, and used to make snacks or hors d'oeuvres, entrees, side dishes, and desserts.
''Phyllo,'' from the Greek, means leaf, and like the word ''leaf'' in English , it also means page, although the culinary phyllo leaves are actually thinner than the pages of a book.
When brushed with butter, filled, and baked, they puff up in flaky golden layers of extra-light pastry.
Phyllo originated in the Orient but was adopted by Greeks, Armenians, and others in the Middle East. In this country, its popularity was once limited to ethnic restaurants, but no more.
The dough was once handmade in storefront shops but is now available in grocery stores and supermarkets.
The commercial phyllo labeled ''thin'' is preferable to ''ultrathin'' for home use. A one-pound box contains from 25 to 28 sheets, and sizes of sheets may vary a little. If fresh dough is not available, look in the frozen bread section at the grocery.
Before buying, inspect the edges of the sheets to make sure they are not crumbled or torn, a sign of improper handling or storage. Phyllo is so thin that it can quickly become dry and brittle when overexposed to air, so always have a slightly damp towel handy before removing it from the package.
Take out the required number of sheets and replace the rest at once, sealing the plastic bag. Store the leaves to be used under a damp cloth until each is needed.
If using frozen phyllo, always thaw it in the refrigerator overnight, then at room temperature for two hours before using. Otherwise, the outside sheets will be sticky and the inner ones still unthawed. If phyllo has been stored in the refrigerator, remove it two hours before using. Beef Wellington 4 1 1/2- to 2-inch slices fillet of beef Butter or margarine 12 sheets phyllo dough 1/4 cup melted butter or margarine 1 egg, well beaten Duxelles (recipe below)
Saute fillets in butter in very hot skillet, 2 to 3 minutes on each side. Season with salt and pepper. Cool completely.
Place first leaf of phyllo dough on damp cloth. Brush with melted butter. Place second leaf directly over first and again brush with melted butter.
Add third leaf. Place one fillet in middle of dough and spread 1/4 of Duxelles over top of fillet.
Fold in sides of dough and wrap like a package, making sure fillet is completely covered. Seal seams with cold water. Repeat for every piece of beef.
Place all on a cookie sheet, seams down. Brush each fillet with well-beaten egg and bake in preheated 375 degree F. oven 15 to 20 minutes, or until golden brown. Serves 4. Duxelles 1 1/2 pounds fresh mushrooms 2 to 3 tablespoons butter or margarine 2 medium onions, or 8 shallots Few drops fresh-squeezed lemon juice Salt and pepper 1/4 cup chopped parsley
Clean mushrooms and trim stems. Chop very fine. Wrap in towel and squeeze out as much moisture as possible.
Heat butter and lightly brown onions or shallots. Add mushrooms, salt, pepper , and lemon juice, then stir over high heat until all moisture has evaporated.
Stir in chopped parsley. Cool completely. Refrigerate in covered jar until ready to use, not longer than 5 days. Broccoli and Cheese Pie 8 phyllo pastry leaves 1/4 cup butter or margarine 1/2 cup finely chopped onion 3 10-ounce packages frozen chopped broccoli, thawed and well drained 3 eggs 1/2 pound feta cheese, crumbled 1/4 cup chopped parsley 2 tablespoons chopped fresh dill 1 teaspoon salt 1/8 teaspoon pepper 1/2 cup butter or margarine, melted
Preheat oven to 350 degrees F.
In 1/4 cup hot butter or margarine, saute onion in medium skillet until golden, about 5 minutes. Add broccoli. Stir.
In large bowl, beat eggs with rotary beater. With wooden spoon, stir in cheese, parsley, dill, salt, pepper, and broccoli-onion mixture. Mix well.
Line inside of 9-inch round pan with removable bottom, or 9-inch spring-form pan with rim in place, with 4 phyllo leaves, overlapping and brushing top of each with melted butter or margarine.
Pour filling mixture into pastry-lined pan. Fold overlapping edges of pastry leaves over top of filling.
Cut 4 9-inch circles from remaining phyllo leaves. Brush each with butter or margarine. Layer one over the other on top of pie. With scissors, cut through leaves to make 8 sections. Pour any remaining butter or margarine over top.
Place on jelly-roll pan to catch drippings. Bake 40 to 45 minutes, or until top crust is puffy and golden. Serve warm. Serves 8.