Knead flour, 50 g sugar, salt, egg yolk and butter in flakes with the dough hooks of the hand mixer. Shape into a ball with your hands and wrap in foil. Chill for 30 minutes. Grease an angular (23 x 23 cm) or round (24 cm Ø) springform pan. Roll out the dough on a floured work surface accordingly.
Place on the bottom of the springform pan. Prick several times with a fork and chill. Grind the Amarettini finely. Separate the eggs. Mix the egg yolks, quark, pudding powder, ground biscuits, 300 g sugar and lemon zest with the whisk of the hand mixer. Beat the egg white until stiff. Fold into the quark mixture in portions. Fill the short pastry into the mould and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: not suitable/ gas: level 2) for 65-75 minutes.
Beat the egg white until stiff. Fold into the quark mixture in portions. Fill the short pastry into the mould and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: not suitable/ gas: level 2) for 65-75 minutes. Loosen the cake edge with a knife, let it cool down in the tin. Serve sprinkled with Amarettini and finely ground pistachios