Place the digestive biscuits into a large resealable bag and crush them finely using a rolling pin, or process them in a food processor until evenly crumbed. Transfer the crumbs to a mixing bowl.

Melt the unsalted butter in the microwave or over low heat and pour it over the crushed biscuits. Mix thoroughly until the crumbs are fully coated.

Transfer the biscuit mixture into a lined 8-inch (20 cm) springform or loose-bottom cake tin. Press the mixture firmly and evenly into the base using the back of a spoon or a flat-bottomed glass.

Place the base in the refrigerator to chill while preparing the filling.

Break the white chocolate into small pieces and melt gently in the microwave in short intervals, stirring between each burst. Set aside to cool slightly.

In a large mixing bowl, whisk together the cream cheese, double cream, pistachio cream, icing sugar, and vanilla extract until the mixture thickens and reaches soft peaks. Take care not to overwhip.

Pour the melted white chocolate into the filling mixture and gently mix until fully incorporated and smooth.

Spoon the cheesecake filling over the chilled biscuit base and spread evenly using an offset spatula or the back of a spoon.

Refrigerate the cheesecake for a minimum of 6 hours, or preferably overnight, until fully set.

Before serving, decorate the cheesecake with swirls of squirty cream, chopped pistachio nuts, and drizzles of melted pistachio cream, if desired.