Put the flour, hazelnuts, egg, fat, sugar and salt in a bowl and knead into a smooth dough with the dough hooks of the hand mixer. Cover and leave to rest in the refrigerator for approx. 30 minutes.
Grease a fruit base mould (24 cm Ø) and sprinkle with breadcrumbs. Press the shortcrust pastry evenly into the mould and prick several times with a fork. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for 25-30 minutes until golden brown.
Turn out the cake base from the mould and let it cool on a cake rack. Let the blackberries thaw on kitchen paper. Remove the seeds from the melon halves and cut out small melon balls with a ball cutter.
Cover the cake with melon balls and blackberries. Mix apple juice and cake glaze, bring to the boil and spread over the fruit. Decorate with lemon balm. Whipped cream tastes good with it.