Quickly knead all ingredients for the shortcrust pastry except cornstarch and flour until smooth. Work flour and cornstarch underneath. Rest the dough in the refrigerator for 10 minutes. Then roll out, cut out a 28 cm ring and place on a baking sheet 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 minutes.
For the frankfurter quantity (sponge cake) melt the butter in a saucepan and bring to the boil once, then remove from the stove. Beat vanilla sugar, sugar, eggs, a little salt and lemon peel in a water bath until warm. Then remove the baking bowl from the water bath and continue beating for 6-8 minutes until cooled. Sift flour and cornstarch on top and fold in. Finally, fold in the melted warm butter.
Pour the mixture into a 28-cup cake springform pan or possibly into a 28-cup ring placed on a baking sheet lined with parchment paper. Bake in a hot oven at 180 °C (convection oven) for 2 min, then turn down to 165 °C and continue baking for approx.18 min.
Cool the bases well. Cut a thin lid from the sponge cake base. (This may be eaten.) Spread the jam on the short pastry. Place the sponge cake on the jam-coated short pastry and form a springform border around the bases.
For the mousse, melt the white cooking chocolate in a water bath (or microwave). D