Put the sultanas, currants and mixed peel in a bowl with the lemon juice, orange juice, and brandy, if using. Mix well, cover and leave to soak overnight.
Heat the oven to 150C/130C fan/gas 2. Line the base and sides of a 20cm round cake tin with baking parchment.
Add the rest of the cake ingredients to the soaked fruit and stir until well combined. Spoon half of this mixture into the bottom of the cake tin and level it off so it's as flat as possible. Roll a third of the marzipan into a circle 20cm diameter and put it on the top. Gently add the rest of the mixture, levelling the surface again.
Bake for approximately 2½ hours until brown, well-risen and firm to the touch. A metal skewer should come out clean when inserted. Allow to cool for 20 mins in the tin and then turn out to cool on a wire rack.
Warm the apricot jam in a small saucepan and brush on the top of the cake. Roll out half of the remaining marzipan to the size of the top of the cake. Press it down firmly and push the edges down with your thumb to crimp it round the sides.
Roll the rest of the marzipan into 11 balls (these represent the Apostles). Place the balls evenly on top of the cake in a circle, sticking them down with a little dab of the jam. Gently blow torch the top of the cake until the balls are a light golden brown, alternatively put the whole cake under a hot grill until the marzipan turns a light golden colour.