Use 2 large baking trays; line with baking paper. Beat eggs and sugar for 5 minutes until pale and fluffy. Finely grate the marzipan paste; fold it into beaten egg mixture with the candied peel.
Mix flour, baking powder and mixed spice and sift over the egg mixture. Knead well to form a smooth dough. On a lightly floured work surface, shape the dough into 60–70 balls, each about 2.5 cm in diameter. Place on baking trays and flatten slightly. Cover; leave in a cool place overnight.
Preheat oven to 160°C. Brush the bases of the biscuits with Kirsch; reserve a few drops for the icing. Bake the biscuits for about 20 minutes.
To make the icing, beat the egg white until stiff; gradually stir in the icing sugar and remaining Kirsch. Dip cookies in the icing and replace on baking tray. Leave to dry for 3–4 minutes in a warm oven.
The cookies will now be very hard. Leave, covered with a cloth, in a humid, warm place to soften for 2 days. Then place in a tin with a slice of fresh bread or a small apple or orange; leave for at least 2 weeks to allow the flavours to develop.