- Preheat the oven to 180°C / 350°F / Gas mark 4. 
- Line an 8inch/20cm square baking tin with greaseproof paper. Set aside. 
- Break the chocolate up into a microwave-safe bowl, and add the butter. Melt in the microwave in 30-second blasts, mixing after each, until completely smooth. 
- In a separate bowl, whisk the eggs and sugar for one minute until pale in colour and frothy. 
- Pour the melted chocolate and butter mixture into the whisked eggs. 
- Add the flour and gently fold everything together until fully combined. 
- Using your hands, break up half of the Biscoff biscuits and stir them into the brownie mixture. 
- Pour half of the brownie mixture in the baking tin and spread out into an even layer. 
- Melt 2 heaped tablespoons of the Biscoff spread in the microwave for 10 seconds. Pour on top of the brownie layer.  
- Pour the remaining brownie mixture on top and spread it out to the edges so that the Biscoff spread is concealed. 
- Either place the Biscoff biscuits on top or break them up and scatter them over the brownie layer. 
- Bake for 18-20 minutes* until the top is no longer shiny and small cracks have started to show around the edges. If you give the baking tin a gentle shake, the brownies should wobble underneath. 
- Leave to cool completely for at least 4 hours or overnight for best results. You can speed this up by putting them in the fridge to set for 2 hours. This will make cutting them easier and make the brownies even more fudgier.