1. Preheat oven to 200°C/Gas Mark 6.
2. Place the frozen berry mix into an oven-proof dish.
3. Mix together in a small bowl 100g caster sugar, mixed spice and corn flour, sprinkle this over the fruit and gently combine.
4. Take the sifted flour, butter and the remainder of the sugar, using a food processor or mixer whiz together for a few seconds on pulse speed until fine crumbs form.
5. Add the yoghurt and whiz again until a soft dough forms (don’t worry the dough will be very sticky). Spoon the mixture in scattered clumps over the fruit; leave some gaps for the cobble effect. Sprinkle with muesli and sugar.
6. Bake for 40 minutes or until pale golden and the fruit is tender.
7. Try adding some sliced Bramley apple or pear to the fruit mix. Delicious served warm with cream or ice-cream.
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