Thaw filo dough according to manufacturers instructions. In some cases, this may be overnight. Preheat oven to 350 F. Brush bottom and sides of deep 10-inch pie dish with some of olive oil. Rince spinach well and place in micro. Proof bowl. Mirco on Hi 1 to 2 min., stirring once, until wilted and cooked thru. (Or, cook spinach in dry skillet until wilted.) When cool enough to handle, squeeze the moisture from spinach. Chop spinach into fine pcs. Place in med. Mixing bowl. Separate 1 egg into 2 small bowls. Break remaining egg into bowl with the egg white and beat lightly. Set both bowls aside. Dice chicken breasts and place in bowl with spinach. Pour in ouzo. Add celery, green onions, mint, basil, marjoram, tarragon, pepper, feta and kasseri. Pour in beaten egg mixture and mix throughly.

Place filo on clean counter and keep covered with plastic wrap or damp towell. Brush sheet with olive oil before placing it in pie dish. Start by placing 1st sheet of filo half of it in the dish and half extending beyond the edge. Place second sheet on top, this time extending over edge in the opposite direction. Place 2 more sheets in a strip at right angles to 1st two, forming a cross. Repeat process with remaining 4 sheets.

Spread the chicken mixture evenly into the pan. Fold overhanging layer of filo up and across chicken, sheet by sheet, brushing with olive oil after each sheet is in place. Finish smoothing out top with a final brushing of olive oil. Beat egg yolk lightly, brush top with beaten yolk.

Pierce top in several places with fork to allow steam to escape.

Bake 50 min., until crust is crisp and golden. Let cool on rack 10 min. Before cutting.

Serve hot or at room temp.