Beat softened butter, powdered sugar, vanilla and salt for approx. 5 minutes until light and fluffy.
Add egg and beat to a homogeneous mixture.
Mix flour with baking powder.
Add the flour mixture to the butter mixture in portions and knead briefly and quickly to form a soft shortcrust dough.
Roll out the dough on a floured sheet of baking paper to a large rectangle (approx. 35 cm x 25 cm in my case) approx. 3 - 4 mm thick and pierce it in several places with a fork.
Pull the baking paper with the dough onto the baking sheet, bake the cake base in a preheated oven at 374 °F (190 °C) for approx. 12 minutes and leave to cool.
Carefully cut a 0.5 cm thick edge off all sides of the cake base and crumble it finely. You will need the crumbs later for the sides of the cake.
Cut the cake base itself into four equally sized, smaller, rectangular cake bases.
Spread three of the cake bases generously with jam and stack them on top of each other.
Place the last cake base on top and spread it very thinly with the jam.
Spread all sides of the cake with the jam.
Chill the cake for approx. 20 minutes so that the jam sets.