Begin by preheating the oven to 160C/ 310/ GM 2 ½ and lightly grease a 7x 7 inch baking tin with butter, then line with baking parchment. Do not grease the baking parchment.
Next measure the butter, sugar, Biscoff spread and syrup into a medium saucepan.
Cook over a moderate heat, stirring frequently until the butter has melted and the sugar has dissolved.
Use a small balloon whisk to beat the ingredients in the pan until they blend together.
Take off the heat, tip in the oats and flour then mix well.
Spoon into the prepared tin, pushing it into the corners and edges. Press the mixture down firmly with the back of a metal spoon.
Bake for around 30 minutes until the edges are golden, then remove from the oven.
Allow to cool in the tin for 10 minutes, then use a sharp knife to mark the flapjack into 9 bars then let cool completely in the tin.
Once cool, pull the flapjack out of the tin, lay it on a sheet of kitchen towel and cut it into portions.
Store in an airtight container for up to 5 days.