Put flour, fat, 50 g sugar, lemon zest and egg into a bowl and knead into a soft shortcrust pastry using the dough hooks of the hand mixer. Wrap the dough in foil and leave to cool for approx. 20 minutes.
Wash the currants, drain and remove the berries from the stalks. Roll out dough between 2 layers of foil to a circle (approx. 30 cm Ø). Put the dough into a springform pan (26 cm Ø) and press the rim.
Prick the pastry base several times with a fork and sprinkle with the breadcrumbs. Cover the dough with parchment paper and sprinkle with the peas. Pre-bake in the preheated oven (electric cooker: 175 °C/ gas: level 2) for about 15 minutes.
Place the cake on a cake rack. Remove peas and parchment paper and let the base cool down a little. Beat egg white and salt until stiff. Sprinkle in the remaining sugar and continue beating the mixture.
Put some berries aside. Mix remaining berries and starch. Carefully fold the berries and nuts into the meringue. Pour the mixture onto the pre-baked base and press in slight dents with the back of a spoon.
Bake in the preheated oven (electric: 175 °C/ gas: level 2) for about 1 1/2 hours. Then let it cool down on a cake rack. Dust the cake with icing sugar and serve sprinkled with the remaining berries.