Preheat the oven to 180°C/fan 160°C/gas mark 4. Grease a 20cm square baking tin and line with baking parchment.
Melt the butter, sugar and golden syrup together in a large saucepan. Stir in the porridge oats and fold through the apple and blackberries.
Pour into the baking tin and bake for 25 minutes until golden. Cut into 16 squares while hot, then leave to cool in the tray.