Via: Dan Jones and Lorenzo Mazzega
Preheat the oven to 190°C/gas mark 5. Grease and line a 20cm square cake tin with baking parchment.
Put the prunes into a bowl and pour over 130ml boiling water. Set aside to soak. Mix the orange zest, juice, apple and sultanas together in a separate bowl.
Put the oats into a mini food processor and whizz to make a fine flour.
Drain the prunes, reserving the liquid, then whizz in a food processor until smooth. Stir the liquid back in, then spoon this mixture into a sieve resting over a bowl, and use a spoon to extract the purée. You should have 140-160g.
Whisk the eggs, honey and oil in a bowl for 3 minutes until foamy, then fold in the prune purée, apple mixture, oats, oil, spelt flour, wheatbran, baking powder and hazelnuts. Fold everything together to combine.
Spoon the mixture into the cake tin, then scatter over the blackberries. Bake in the oven for around 40 minutes, until a skewer inserted into the centre comes out clean. Cool on a wire rack, then cut into 20 squares and serve.
Skin by Liz Earle (£25, Orion Spring)