Mix the flour, sugar, lemon zest and salt in a bowl. Add the butter and rub together using your hands to form an even, crumbly mixture. Add the egg and egg yolk, mix quickly to create a soft dough – do not knead. Flatten the dough, cover and chill for approx. 30 mins.
On a surface lightly dusted with flour, roll out 2/3 of the dough to approx. 3 mm thick and transfer to the prepared tin. Prick firmly with a fork. Spread the jam over the top. On a lightly floured surface, roll out the remaining dough to approx. 3 mm thick, cut into strips and place on the jam in a lattice pattern, press down the edges firmly.
Brush the crostata with egg. Bake for approx. 25 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, leave to cool on a cooling rack.