Slice the apples and mix with the sugar and lemon peel. With a small sharp knife, scrape the vanilla seeds from the bean and add to apples. Vacuum pack in a boilable pouch. Steam over boiling water for 10 to 15 minutes, or until soft to the touch. Remove and drop into icy slush until completely cold, about 30 minutes. Keep apples in the pouch in the refrigerator until ready to use. (The apples will keep for up to 1 week.) Drain off liquid before using. Alternatively, combine apples with sugar, vanilla, and lemon zest in a heavy saucepan. Cover and cook over very low heat until the apples are soft, about 20 minutes. Let cool; drain just before using.
Pit the Armagnac-soaked prunes. Cut into ½-inch pieces and return to ¼ cup of the prune-Armagnac syrup until ready to use.
Mix 2 tablespoons of the melted clarified butter with the orange-flower water, 1 tablespoon sugar, the remaining 1 tablespoon prune-Armagnac syrup, and the Armagnac.
Two to 3 hours before serving, place a baking stone or heavy baking sheet on lowest oven rack. Preheat the oven to 400°F. Lightly brush a 15-inch round pan, such as a pizza pan (preferably with a black finish) with 1 tablespoon of the remaining clarified butter.
Unroll the strudel or phyllo leaves in front of you and cover with a damp towel. Working quickly (this pastry dries out fast when exposed to air), brush the top leaf lightly with melted clarified butter. Fold in half lengthwise and brush each side lightly with butter. Place one end of the folded leaf in the center of the pan, letting the sheet hang over the side of the pan (Figure ). Repeat with the remaining leaves, arranging them spoke fashion so that the inner ends are stacked in a hub and the outer ends barely touch (Figures and ).
Very lightly sprinkle some of the reserved scented butter-liquid over the dough that extends over the edge of the pan. Place drained pitted prunes in a 10-inch circle in the center of the pastry. Top with drained cold apples.
To enclose the filling, start with the last leaf placed on the pan. Lift up the outer end and bring it toward the center, twisting the piece once so that the underside faces you. Roll up the end of the strip loosely to form a cup-shaped “rose” and set it flat on the filling, pressing lightly so it adheres (Figure ). Repeat with the remaining leaves, placing the flowers close together to cover the top of the cake. (Do not worry if a little filling shows through.) Sprinkle the top very lightly with the remaining scented butter-liquid, drizzle with the remaining clarified butter, and dust with 3 tablespoons granulated sugar (Figure ).
Place the pan in the oven on hot baking stone or baking sheet and bake for 12 minutes. Reduce the oven temperature to 350°F. Bake for 20 to 25 minutes longer, or until the croustade is golden and crisp. Slide onto a wire rack. Sprinkle 2 more tablespoons granulated sugar over the top and let cool to lukewarm. Just before serving, dust with confectioners' sugar.
Strudel leaves are stronger and fewer to the pound than phyllo leaves. They do a better job of keeping the “roses” rigid after shaping, but if you can buy only the thinner phyllo leaves, that won't lessen the rustic charm of this wonderful, easy cake.
If you prepare the cake early in the day and wish to prevent the bottom layer of pastry from becoming too wet, use stale sponge cake or stale white bread crumbs mixed with a little sugar between the bottom leaves of the pastry. This makes an excellent foil for absorbing the moisture of the fruit fillings.