Mix the flour, almonds, sugar and salt in a bowl. Add the butter and rub together using your hands to form an even, crumbly mixture. Add the lemon zest and egg, and mix quickly to create a soft dough – do not knead. Flatten the dough, cover and chill for approx. 30 mins.
On a lightly floured surface, roll out the dough to approx. 2 mm thick (approx. 40 x 35 cm), place on a baking tray lined with baking paper. Prick the dough firmly with a fork. Spread the jam and apple slices on top of the dough, top with the butter and sprinkle with sugar.
Approx. 40 mins. in the lower half of an oven preheated to 200°C. Remove from the oven, allow to cool slightly, slide the tart onto a cooling rack along with the baking paper, leave to cool completely. Dust with icing sugar.