Put flour, sugar, lemon zest and salt into a mixing bowl and mix well. Press a depression in the middle. Warm the milk and mix with crumbled yeast. Pour into the flour bowl, mix with some flour and leave to rise covered in a warm place for 15 minutes.
Add the egg and mix the ingredients with the dough hooks of the hand mixer until the dough comes off the bottom of the bowl as a lump. Cover and leave to rise in a warm place for 30 minutes. Drain gooseberries well on a sieve.
(Collect the juice and use it elsewhere.) Crumble the rusks. Knead the dough again. Grease baking tray (30 by 40 centimetres) and dust with flour. Roll out the dough with the dough roller on the baking tray and press the edges of the dough a little higher.
Leave to rise on the baking tray for another ten minutes. Sprinkle crumbs on the dough, spread gooseberries on top. For the icing, stir the fat and sugar until frothy. Add the eggs bit by bit. Stir in flour, cream, cinnamon and salt.
Spread the icing on the cake by the spoonful as a blob. Bake in the preheated oven (electric: 200°C/ gas: level 3) for 30 to 35 minutes.