Heat oven to 180C/160C fan/gas 4. Oil and line a 20cm x 30cm baking tin with baking parchment. Beat the butter and sugar with most of the lemon zest until pale and fluffy. Add the eggs one at a time, mixing constantly, then add the flour, almonds and baking powder, and keep mixing until you have a smooth cake batter. Stir in the milk and dried fruit.
Scrape half the cake batter into the tin and level the surface. Coarsely grate half the marzipan onto the batter to create an even layer, then cover with the rest of the batter, trying not to disturb the marzipan too much. Level the top and bake for 35-40 mins or until a skewer inserted into the centre comes out clean. If any wet cake mixture clings to the skewer, return the cake to the oven for 5 mins, then check again. Mix the remaining caster sugar with a quarter of the lemon juice, then drizzle over the cake while still warm. Leave the cake to cool in the tin.
Mix the icing sugar with enough lemon juice to make a drizzly icing – 2-3 tsp should be enough. Divide the rest of the marzipan into 11 even lumps and roll into balls. Drizzle the icing over the cake, top with the marzipan balls and sprinkle with the remaining lemon zest. Will keep in an airtight container for up to five days.