Preheat your oven to 350F/180C.Butter and Line an 8*8 inch square pan with parchment paper, leaving a 2 inch overhang on the sides and set aside.

In a bowl, whisk together the flour, baking soda, and salt.

In the bowl of your electric stand mixer, fitted with the paddle attachment or with a hand mixer beat the butter, sugar and vanilla extract until light and frothy (about 2 to 3 minutes). Beat in the egg for 2-3 mins. Then, on low speed, beat in the flour mixture until incorporated. Fold in the chopped cookies.

Melt the dark chocolate and butter in a large heatproof bowl, placed over a saucepan of simmering water or in a microwave in 30 second intervals. Set aside to cool slightly.

In the bowl of your stand mixer or a bowl using a hand mixer beat the eggs and sugar for 3-4 minutes until pale. Add the melted chocolate/butter and beat in well. Next, beat in the vanilla extract.

Finally, stir in the flour, cocoa powder and salt.

Pour the blondie batter into the prepared pan followed by the brownie batter. Drop dollops of cookie butter on top of the brownie batter and make swirl using a knife or toothpick.

Place a few biscoff cookie on top and bake for 25-30 mins until a toothpick inserted into center comes out clean.

Let the bars cool completely before cutting into pieces.