Line a rectangular tin (approx. 24x13cm) with baking paper.
Crush Biscoff biscuits into fine crumbs using a food processor (or place in a ziplock bag and crush with a rolling pin). Mix with melted butter until well combined.
Press the mixture firmly into the base of the tin and leave in the fridge while you make the caramel.
In a saucepan, combine the condensed milk, brown sugar, butter and Biscoff spread
Stir continuously over medium heat for 5–7 minutes until the mixture thickens. Pour the caramel over the base and smooth it out. Leave in the fridge for 20 minutes before adding the chocolate.
Melt the chocolate and Biscoff together in the microwave. Pour over the caramel and spread evenly. Drizzle extra Biscoff spread on top and swirl with knife - microwave it for 10–15 seconds to make it runny.
Leave in the fridge for 4-5 hours for the caramel and chocolate to set.
Once set, remove from the tin and cut into 10 pieces using a hot knife (to prevent the chocolate from cracking).
Enjoy - store in an airtight container in the fridge.