Pre-heat your oven to 160C Fan/180C/400F/Gas Mark 6, line a swiss roll tin or a baking tray with a lip, with baking paper. The one I used was a Wilton tray that is 33.7 x 23.5 cm (13.25 x 9.25 inches)
For the sponge, whisk the eggs and sugar together with an electric whisk or in a food mixer for around 8 minutes until it reaches 'ribbon stage' - this is when you can drizzle the mixture in a figure 8 and it takes at least 3 seconds to sink back in. It will also be very light in colour and have doubled in size
Add the vanilla and whisk a little to mix it in
Gently fold in the flour, ideally using a metal spoon, trying not to lose the volume
Pour into the tin, and spread the mixture around. Bake for 12 minutes
Remove from the oven and tip onto a clean sheet of baking paper
Remove the baking paper the sponge was baked with, then roll up the sponge, taking the clean baking paper with it, then leave to cool completely
Gently unroll the sponge and spread a layer of melted Biscoff spread all over it. It's much easier to spread the Biscoff when it's melted, so pop it in the microwave for 10-20 seconds to melt it first
Whip up the cream with the icing sugar and vanilla
Spread most of the double cream (save some to decorate the top) over the Biscoff spread
Re-roll the sponge as tightly as you can, and place onto a serving plate
Melt the Biscoff spread for decoration and drizzle it all over the swiss roll
Pipe the remaining whipped cream on top, then add the biscuits (they will go soft from being in contact with the cream so add right before serving). I also crushed up some of the biscuits and sprinkled over some crumbs
Serve immediately, store any leftovers in the fridge for 2-3 days