For the blueberry slices, beat eggs, sugar, salt, vanilla sugar and lemon zest until very foamy. Slowly beat in oil. Fold in flour mixture. Place 24 x 24 cm square baking frame on a baking sheet and pour in the batter.
Bake at 180 °C for 20-25 minutes. Let the finished sponge stand for 5 minutes, remove the baking frame and clean it. Turn the sponge cake over on a cake plate with the baking frame.
For the cream, whisk Qimiq until smooth. Stir in curd, sugar and a little lemon juice until well blended. Spread jam on the sponge cake base and spread the cream on top. Place in the refrigerator for 2 hours.
Top with blueberries and glaze with cake glaze. Refrigerate again until cake glaze is firm. Loosen baking frame and cut into 9 slices.