Put the rhubarb, sugar and orange juice in a covered pan and gently cook or 5 minutes.
Add blackberries and heat through until rhubarb cooked.
Transfer to an ovenproof dish.
Set the oven to 200⁰C.
To make the cobbler put the flour, pinch of salt and baking powder in a bowl and mix well with a whisk.
Add the yogurt and mix to a dough with you hand.
On a floured surface roll out to a 25cm square.
Mix grated marzipan, cinnamon and Demerara sugar together and sprinkle evenly over the dough.
Roll the dough up tightly and cut into 12 equal sections with a sharp knife.
Bake for 15 – 20 minutes until cooked and golden.
Serve hot with custard or ice cream.