Instructions: Preheat the oven to 375 degrees. Thoroughly scrub the celery root, trim off a thin piece from both ends and peel; set aside the trimmings. Thinly slice the celery crosswise, then cut into 1/4-inch dice. Transfer to a nonreactive bowl and cover with cold water to prevent discoloration. Trim the root end and the dark green portion of the leeks; set aside. Coarsely chop the remaining white and tender green portion of the leek and rinse well but dont dry. Trim off the mushroom stems and set aside. Slice the mushroom caps crosswise 1/2-inch thick. (Use the celery root trimmings, leek trimmings and mushroom stems to make the Mushroom Sauce.)

In a large nonreactive skillet, heat 2 tablespoons of the oil oer low heat.

Using a slotted spoon, transfer the diced celey root to the skillet. Add the chopped leeks and onion. Squeeze half a lemon over the vegetables, add the tarragon and cook until the liquid is evaporated and the vegetables are tender and just beginning to brown, about 12 minutes. Season with salt and pepper. Transfer the mixture to a nonreactive bowl.

In the same skillet, heat the remaining 1 tablespoon oil over high heat until it starts to shimmer. Stir inthe mushrooms until coated with oil, then squeeze the remaining lemon half over them. Cook until the mushrooms begin to color, about 2 minutes. Season with the parsley and salt and pepper. Remove from the heat and stir in the celery root mixture. Fold in 1/2 cup of the Mushroom Sauce, teh creme fraiche and the Parmesan.

On a lightly floured baking sheet without sides, roll out the galette dough into a 14-inch round. (Alternatively, divide the dough into 4 even pieces and roll into 8-inch rounds.) Spread the filling over the dough, leaving a 2-inch border. Fold up and pleat the border of the dough. Brush the dough with the beaten egg. Bake the galette until golden, about 30 minutes for Yeast Dough and 40 minutes for Pie Dough.

To serve, pour 1/4 cup of the Mushroom Sauce over the top of the Mushroom Sauce over the top of the galette. Garnish with chopped parsley. Cut the galette in wedges and spoon some of the sauce over each one.

Way," "The Greens Cookbook" and the forthcoming "The Vegetarian Joy of Cooking" (all by Bantam).

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