Put the bowl of the ice cream machine into the freezer overnight prior to making the ice cream, or preferrably for 24 hours.

The next day, boil cream, milk, half of the sugar (20g), and vanilla paste in a saucepot until bubbles start to break the surface. Turn off the heat. The temperature should be around 80°C here.

Meanwhile, beat the egg yolks and remaining half of the sugar until pale.

Gradually add a small amount of the cream and milk mixture into the egg yolk mixture to temper the egg yolks (to slowly warm up the egg yolks, preventing them from coagulating). Pour this mixture back into the pot, and cook over low heat for a few minutes until mixture becomes thick enough to coat the back of a spoon. The temperature should be around 70-75°C here.

Strain the mixture into a bowl that is put into an ice water bath. Once the mixture has cooled, put in the refrigerator for at least 1-2 hours before putting into the ice cream machine. If your ice cream machine is a very powerful one, you don't have to refrigerate your mixture.

Take the bowl out of the freezer and place it into the ice cream machine. Pour the mixture into the bowl along with Speculoos cookie butter and turn on the ice cream machine to churn the mixture for about 20 minutes, until the liquid mixture becomes ice cream. Add biscoff cookie crumbs into the mixture towards the end (at around the 18-minute mark).

Transfer ice cream to a container, and keep in the freezer for at least a few hours before eating. The ice cream will be harder if frozen overnight.