Combine the dried fruit, walnuts, almonds, orange rind and mixed spice in a large heatproof bowl.
Place caster sugar in a saucepan over medium heat. Cook, stirring occasionally, for 5 mins or until sugar melts and caramelises. Remove from heat. Slowly and carefully add orange juice (mixture will bubble). Place over low heat and cook, stirring occasionally, for 5 mins or until the hard toffee dissolves. Remove from heat. Add the sherry, brandy or whisky, or apple juice, and stir to combine. Carefully pour the hot liquid over the fruit mixture. Stir to combine. Cover with plastic wrap and place in the fridge, stirring occasionally, for 1 day or until liquid is absorbed. (To develop the flavours, do this up to 1 month ahead.)
Preheat oven to 150°C. Grease a 20cm round cake pan and a 15cm round cake pan. Line the bases and sides with 3 layers of baking paper, allowing the sides to extend 6cm over top of the pans.
Use an electric mixer to beat the butter and brown sugar in a bowl until pale and creamy. Add the eggs, 1 at a time, beating well after each addition. Add to the fruit mixture and stir to combine. Add flour and stir to combine. Divide among prepared pans. Smooth the top of each cake with a palette knife. Tap each cake pan on a work surface 3 times to settle the mixture.
Bake the cakes for 3 hours or until a skewer inserted in centre of 15cm cake comes out clean. Bake the 20cm cake for a further 30-45 mins or until a skewer inserted in centre comes out clean.
Brush the top of each hot cake with extra sherry, brandy or whisky, or apple juice. Cover with foil and invert cakes, still in the pans, onto a clean work surface (this helps flatten the tops). Set aside overnight to cool completely.
Place on a serving plate and dust with icing sugar.