Preheat the oven to 190°C/Fan 170°C/Gas 5. Line 2 baking trays with baking parchment.
Melt the golden syrup and butter together in a saucepan over a gentle heat. Remove from the heat and beat in the brown sugar and egg yolk.
Sift the dry ingredients into a bowl. Add the wet ingredients and mix thoroughly. You might think the dough is too dry at first, as it will be very crumbly, but using your hands, keep working it together until it is smooth.
With your hands, roll dough into balls (about 25g) then place them – spaced well apart, as they will spread – on the baking trays. Bake in the oven for 10-12 minutes until the biscuits are a rich golden brown and are cracked on the surface.
Remove the biscuits from the oven. They will be very soft, but don’t worry, they will firm up very quickly. As soon as they are firm enough, transfer them to a cooling rack with a palette knife.