Pre heat the oven to 180 degrees C / 356 F. I use an electric fan oven, please adjust according to your own oven.Line a square cake tin with parchment paper.
Add the sultanas to a small bowl then cover with the orange juice, leave for as long as you can so the sultanas soak up the juice and get nice and plump.
Melt the butter and golden syrup in a medium pan over a low to medium heat. As soon as the butter melts turn off the heat.
In a large bowl mix together the oats, nuts, cinnamon, seeds and sultanas. Pour the melted butter and syrup over the oat mix then stir well. Making sure everything is coated in the butter and syrup.
Tip the oat mix into the prepared cake tin, then push it down with the back of a large spoon. Score the flapjack mixture with a sharp knife into 8 or 16 portions.
Place the tin on the middle shelf of the over and bake for 20 to 25 minutes, turning halfway through baking. The flapjacks should be golden brown. Leave to cool slightly in the tin. Lift the paper containing the flapjacks and transfer to a cooling rack, leave to cool completely before cutting.
Store in an airtight container for up to a week.
For this post I have cut the flapjacks into larger bars, I usually serve them in squares, which would result in 16 portions.