Add butter, light brown sugar, lemon zest, lemon juice and golden syrup to a mixing bowl and melt. I usually melt in the microwave over a medium to high heat. Be sure to stop constantly after every 10 seconds or so and mix each time.
Add the porridge oats into the melted mixture and mix together until thoroughly combined.
Pour the flapjack mixture into a lined 9″ square baking tray. Make sure to spread the mixture evenly into all four corners. Bake in the oven for 20 minutes
Once baked, leave the flapjacks to cool before cutting them into slices