For the honeycomb: Line a 8x10in baking tin with baking paper and grease the paper with butter. Mix the sugar and golden syrup in a deep saucepan and place over a medium heat. Once all the sugar has dissolved, turn up the heat and simmer until the caramel turns an amber colour. Immediately add the bicarb, and beat with a spatula to fully incorporate. The mixture will be foaming and very hot, so be careful! Scrape straight away into the prepared tin and leave to harden at room temperature. This will take about an hour.
For the base: Line the base of an 8″ high sided, loose-bottomed or spring form tin with baking paper. Blitz the digestives in a food processor until fine crumbs. Then add the melted butter and blitz again until it starts to hold together. Tip this into your lined tin, and using a spoon (or your hands), compact the base down. Then chill in the fridge for 20 minutes.
For the cheesecake: Break up the cooled honeycomb and place around half into a food processor. Blitz until a fine crumb, and set aside, making sure you have 100g. If not, blitz more until you have the correct amount.
Using an electric hand-whisk beat the cream cheese and icing sugar together in a large bowl. Then whisk in the double cream until the mixture thickens. Finally, stir in the ground honeycomb until fully combined. Pour half of the mixture on top of the chilled base and level out. Then spread the Biscoff spread on top in an even layer. Finally, top with the remaining cheesecake filling and level out carefully. Then cover and leave in the fridge overnight or for at least 4 hours.
For the decoration: Just before serving, melt the Biscoff spread and using a teaspoon drizzle around the edges in a circular pattern. Then scatter over some of the remaining honeycomb pieces/crumbs.
Cheesecake is best served straight from the fridge and can be kept in an air-tight container in the fridge for 4-5 days - however, please note that the honeycomb decorations will dissolve in the fridge, so decorate just before serving.