Halve, pit, and chop nectarines and, in a heavy saucepan, combine them with sugar and 1/2 cup water. Bring to a boil, stirring, and cook it at a slow boil, stirring occasionally, for 15 minutes. In a food processor, puree the mixture and force it through a fine sieve into a large bowl, pressing hard on the solids. In a small saucepan, sprinkle gelatin over the lemon juice and schnapps, let it soften for 5 minutes, then heat mixture over low heat, stirring, until gelatin has dissolved. Stir gelatin into nectarine puree, blending the mixture well. Let it cool to room temperature. In a chilled bowl, beat the cream until it holds soft shapes, (not as stiff as soft peaks) and fold it into the nectarine mixture. Trim the Genoise and cut it into three layers, horizonally. Peach Syrup: In a small saucepan, combine the sugar and 1/4 cup water. Bring to a boil, stirring until sugar is dissolved, and stir in the schnapps. Let the syrup cool to room temperature. Assembly: Center one layer in the bottom of a 9-1/2-inch springform pan and brush with half the peach syrup. Pour half the mousse over the cake and top it with another layer of Genoise. Brush with the remaining peach syrup and pour the remaining mousse over the cake, rapping on the side of the pan to expel any air bubbles and smoothing the surface. Chill for 2 hours, or until it is set. Peach Glaze: In a small bowl, sprinkle gelatin over 3 Tbsp cold water and let it soften for 5 minutes. In a small saucepan, combine the preserves and schnapps, bring mixture to a boil, stirring, and simmer it for 1 minute. Remove pan from heat, add gelatin mixture, stirring until gelatin is dissolved, and strain the mixture through a fine sieve into a bowl, pressing hard on the solids. Assembly: Pour all but about 2 Tbsp of Peach Glaze over top of the mousse cake, covering it completely, and chill the cake for 2 hours, or until glaze is set. While cake is chilling, in a food processor, grind the remaining Genoise layer into fine crumbs. Toast the crumbs in a jelly-roll pan in a preheated 350f oven for 5-8 minutes or until they are golden. Reserve. Cut half the nectarine into thin slices, and arrange them decoratively on top of the cake in a pinwheel pattern. Brush the remaining glaze over the nectarine slices and chill the cake, covered, for 1 hour, or until the newly applied glaze is set. Run a thin knife around the edge of the pan and remove the side of the pan. Working over a sheet of wax paper, coat sides of cake with the cake crumbs. Let cake stand at room temperature for 20 minutes before serving.