Make a shortcrust pastry from the dough ingredients, wrap in foil and refrigerate for about 1 hour. Line a sheet (39 x 26 cm) with baking paper, roll out the dough, place on the sheet and prebake at 180 ° C (preheated) for 10-12 minutes.
In the meantime, prepare the walnut foam. Beat the egg whites with the sugar until stiff and carefully fold in the ground walnuts.
Spread the jam on the dough base, spread the walnut foam evenly over it and smooth it out. Bake at 170 ° C for another 20-30 minutes.
To cut open, keep dipping the knife into hot water and wiping it clean.