Put the South African Flame raisins and glacé cherries into a large mixing bowl. Cover with boiling water and leave for 2-3 minutes. Drain through a colander. Tip the fruit back into the bowl and add the rum, stirring well. Cover and leave in a cool place for up to 2 days, though at least overnight. This plumps up the fruit and makes the cake deliciously moist.
Preheat the oven to 170°C/Gas Mark 3. Grease and line a 20cm (8in) round cake tin with double-thickness baking paper.
In a very large mixing bowl, beat together the butter and sugar until light and fluffy, using a wooden spoon or hand-held electric mixer. Gradually add the beaten eggs, beating well between each addition. Stir in the almonds, orange zest and orange juice.
Sift the flour, salt and ground mixed spice into the mixing bowl, folding them through with a large metal spoon. Do not beat the mixture at this stage. Add the soaked raisin mixture and stir it in thoroughly. Spoon the mixture into the prepared tin, leveling the surface. Remember that the mixture will not rise.
Bake for around 2 hours in the centre of the oven. Test for doneness by inserting a fine skewer into the centre – it should come out clean. If not, cook for a little longer. Stand the cake on a wire rack and leave it to cool in the tin. When completely cold, spoon 3 tbsp dark rum over the top and let it soak in. Wrap in greaseproof paper. Store in an airtight tin in a cool place for up to 3 months.