Preheat the oven to 170°C (fan) / 350°F / Gas Mark 4. Line a baking tin with baking parchment or greaseproof paper - mine was 18cm x 24cm but anything roughly the same size will be fine.
In a large bowl, combine all the dry ingredients - sifting the flour and cocoa.
Mix together the wet ingredients then add them into the bowl with the dry ingredients. Mix together until fully combined, thick and glossy.
Add the chocolate chips to the brownie mix and stir well.
In a small bowl or mug, heat the Biscoff spread in the microwave for 20 seconds until just melted. Drizzle it over the brownie mix.
Break the biscuits into chunks (or leave them whole if you prefer) and press them down into the brownie mix.
Bake the brownies for 35-40 minutes until just set in the centre, but still soft. Remove from the oven and leave to cool in the tin.
When fully cooled, remove from the tin. At this point you can chill the brownies to make slicing easier, (but bring them back to room temperature to serve). Slice into small-ish squares and enjoy!
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Notes
Chill the brownies before slicing to get nice neat and clean lines, but if you have time, let them get back to room temperature before serving.Use a bread knife or other serrated knife to slice neatly through the biscuit layer and the fudginess underneath!Adjust the baking time to suit your brownie preference - 5 minutes less in the oven makes a very moist, fudgy brownie. 5 minutes more gives more of a cake-y texture.