Preheat the oven to 180°C (350°F) and line two baking trays with baking paper.
Cream the butter, brown sugar and icing sugar together.
Add in the eggs and vanilla and beat until light and fluffy.
Beat in the cornflour, flour and baking soda and mix until all combined into a soft dough.
Stir in the chocolate chips.
Dollop in the Biscoff spread and lightly fold the spread in the dough. Only a few times. You want to see cookie butter swirls, not mix it into the dough.
Roll into balls and place on the tray leaving at least 1 and ½" between each cookie to allow for spreading.
If the dough is too soft, chill the dough for 1 hour before baking.
Bake for 10 minutes. They will look under done but the harden as they cool.