Place the butter, syrup and dark brown sugar in a large heavy pan and simmer over a gentle heat until the butter and sugar have melted. Add the oats, currants and salt to the pan and stir well so that all the oats are coated in the syrup

Tip the mixture into the lined pan and spread out in an even layer using a spatula or the back of a large spoon

Bake in the oven at Gas Mark 4 for 30 minutes until the top of the flapjack is golden brown. Remove from the oven and leave to cool completely. When cool remove the lining paper and cut the flapjack into 24 squares. Store in an airtight container until needed. The flapjack will store for at least 5 days