Several hours or day before serving, prepare Fresh Pasta: In large bowl or food processor fitted with chopping blade, combine 2 1/4 cups flour and the salt. In 1-cup measuring cup, beat eggs, 2 tablespoons water, and the oil until well mixed; stir into flour mixture. Or, with food processor blade whirling, add egg mixtrue through the feed tube. Dough should form a ball. If it isi too sticky, add more flour; if it is too dry, add more water. On lightly floured surface, knead dough a few minutes or until smooth. Wrap with plastic wrap; refrigerate 1 hour or overnight.

Prepare Mushroom Sauce: In small bowl, combine boiling water and porcini; set aside 20 minutes. In 6-quart saucepot, heat oil over medium heat. Add carrot, celery, and onion; saute, stirring constantly, until tender but not browned. Stir in chopped mushrooms , tomato puree, garlic, and salt; heat to boiling over high heat, stirring constantly. Drain porcini, discarding liquid. Rinse porcini and add to mushroom-tomato mixture. Reduce heat to low and cook mixture 45 minutes, stirring occasionally. Cool to room temperature and assemble lasanga or cover sauce and refrigerate overnight.

Prepare White Sauce: In heavy 2-quart saucepan, melt butter over medium heat. Stir in flour, salt, and nutmeg; cook until bubbly. Gradually stir in milk and heat to boiling, stirring constantly. Cool to room temperature and assemble lasagna or cover and refrigerate overnight.

About 2 hours before serving or day before (if baking ahead and reheating), in 6-quart saucepot, heat 3 inches water to boiling. Divid pasta dough into 5 pieces. On lightly floured board, roll out 1 dough piece to fit 3 1/2-quart (3-inch deep) redware or 13- by 9-inch glass baking dish. Add pasta sheet to boiling water being careful that it does not fold over. Boil 3 minutes. With 2 slotted spoons, transfer pasta to oiled colander on tray. Repeat with remaining 4 pieces, separating pasta sheets with pieces of aluminum foil that have been oiled on both sides.

Heat oven to 375°F. Assemble lasagna: Rub softened butter over bottom of baking dish. Top with 1/2 of mushroom sauce, 1 sheet pasta, 1/2 or white sauce, 1 sheet pasta, 1/2 cheeses, and 1 sheet pasta; repeat, ending with the cheeses. Bake 45 minutes or until the top is golden brown. Check after 30 minutes and cover top with aluminum foil if it browning too quickly.

If baking a day ahead, cool lasagna completely, cover tightly, and refrigerate. To reheat, heat oven, to 350°F. Cover top of lasagna tightly with aluminum foil and bake 1 1/2 to 1 3/4 hours or until center is hot. To serve, cut into 12 pasta-course or 8 main-dish servings.

dish ahead. One is to prepare and refrigerate the components a day ahead and assemble and bake the lasagna about 2 hours before serving it. Another calls for preparing, assembling, and baking the dish a day ahead and then reheating it before serving.