First, preheat your oven to 180°C (350°F).
Next, put 175g of unsalted butter, 175g of golden caster sugar, and 175g of golden syrup into a pan over low heat. (Remember that you can use honey or agave syrup instead of golden syrup if you prefer.)
175 g Butter or Margarine, 175 g Golden Syrup, 50 g Demerara Sugar
Stir the mixture continuously until the sugar dissolves and the butter melts. (Be careful not to let it boil or burn.)
Once the mixture is smooth, remove the pan from the heat and add 350g of rolled oats. Mix well until the oats are coated evenly.
350 g Oats
Pour the mixture into a baking tin lined with parchment paper, spread it evenly, and press down firmly. (You can use the back of a spoon or your hands to do this.)
Bake the flapjacks in the preheated oven for 25-30 minutes or until they turn golden brown. (Do not overcook or they will become hard and dry.)
Remove the flapjacks from the oven and let them cool in the tin for at least 10 minutes, then transfer them to a wire rack to cool completely. (Do not attempt to cut them while still hot as they will crumble and break.)
Once cooled, cut the flapjacks into squares of your desired size. (I usually opt for 2x2 inch squares.)