Preheat the oven to 160 degrees C/325F and grease a 9x9 in pan.

Place the butter and sugars into a large bowl or the bowl of your stand mixer and beat until light and fluffy, about 2 mins on med-high speed.

Add the vanilla extract and flour and mix until a soft dough forms.

Place around a 1/3 of the dough into the greased pan (wrap remaining dough in cling film and refrigerate) and bake for 12-14 minutes, until puffy and ever so slightly firm to the touch.

Allow the base to cool for 15 minutes.

Once cooled, spread the Biscoff over the base, leaving a 1/4 inch gap around the edge.

Crumble the remaining dough over the top of the Biscoff and bake for 20-25 minutes, until puffy, very lightly golden and slightly firm to the touch.

Allow to cool completely before removing from pan. Slice into 12-15 bars.

Bars will keep in an airtight container, at room temperature for 3 days.