Preheat the oven to 180°C.
Finely chop the hazelnuts then mix with the flour and oats.
Heat the butter with the golden syrup and sugar. When the sugar is melted, take it off the stove and pour over the cereal mixture. Combine well with a flat wooden spoon.
Grease & line a 23 cm square baking tin, then spoon the batter into it, spreading out evenly. Using a spoon press down the mixture.
Bake for about 20 minutes until golden brown – be careful not to burn the top!
Allow the tin to cool, then lift the cake out and let it cool completely before slicing into flapjack with a sharp knife. Keep the flapjacks in an airtight container.