Preheat the oven to 180c.
Either on the hob or in a microwave: melt the butter until runny. Stir in the golden syrup. Then stir in the sugar. Continue to stir until sugar is completely dissolved.
In a bowl weigh out the oats and stir in the syrup mix.
Line a rimmed baking tray 20x20cm with foil.
Empty flapjack mix into baking tray and press down all the mixture evenly to 1-2cm high.
Cook in the oven for about 30 minutes or until golden brown.