Heat oven to 180C (or 160C for fan ovens). Line a baking tin (9×9 inch square) with paper.
In a big bowl, mix melted butter, sugars until smooth. Then beat in eggs and vanilla until smooth again.
Add flour and cornflour, mix well to make a thick batter.
Fold in white chocolate chips.
Pour batter in the tin, spread it out. Add dollops of biscoff spread, swirl it a little.
Sprinkle chopped biscuits on top.
Bake for 25-30 minutes (or more) until the middle is slightly wobbly.
Let it cool completely before eating. You can cool it in the tin or on a wire rack. (For a better texture, you can chill it in the fridge for an extra hour.)
