Shortcrust pastry: Quickly knead all ingredients until smooth. Rest the dough in the refrigerator for about 30 minutes. Roll out the dough, cut out a ring of about 26 cm and place on a baking tray lined with parchment paper.
(Leftover dough can be frozen without any problem.) Prick the dough a few times with a fork and then bake in a hot oven at 180 °C for 10 min.
Frankfurter quantity (sponge cake): Melt the butter in a saucepan and let it boil once, then pull it from the kitchen stove. Beat the vanilla sugar, sugar, eggs, a little salt and lemon zest briefly in a bain-marie until warm, then remove the baking bowl from the bain-marie and continue beating for 6-8 minutes until cooled. Sift flour and cornstarch on top and fold in. Finally, gently fold in the warm melted butter.
Fill the amount into a 24 cake springform pan or possibly into a 24 ring, which is placed on a baking sheet lined with parchment paper. Bake in the oven heated to 180 degrees (convection) for 2 minutes, then turn down to 165 degrees and continue baking for about 18 minutes. Cool the sponge well and then cut horizontally into two slices.
Orange mousse: Stir well orange juice, juice of one lemon and 60 g powdered sugar and let it boil once. Soak gelatine in cold water, then squeeze and let it melt in the orange juice. Cool slightly and add the orange liqueur at room temperature. Just before the mousse sets, fold in the whipped cream.
Mocha mousse: