Line an 8x10-inch tin (or 8x8 for thicker slices) with baking paper.
In a large bowl, crush the Biscoff biscuits and Digestive biscuits into medium-sized chunks. Stir in the white chocolate chips if using.
Break the milk chocolate into pieces and add it to a pan along with the butter, golden syrup and cocoa powder. Melt gently over low heat.
Pour the melted mixture into the bowl with the crushed biscuits and chocolate chips. Mix well until all the biscuits are coated in chocolate then press the mixture into your lined tin.
Melt the white chocolate and spread it evenly over the top of the traybake.
Melt the Biscoff spread in the microwave for 10-20 seconds until runny. Drizzle it over the white chocolate topping then use a toothpick to create a swirly pattern. Top with 9 whole Biscoff biscuits.
Refrigerate the whole thing for 2 hours until firm. Then just cut into slices and enjoy!