Whizz the digestive biscuits in a food processor to make fine crumbs. Combine with melted butter and a tablespoon of sugar, then press into the base of a 9-inch springform cake tin, and refrigerate to set.
In a small blender, crush the blackcurrants till you get a smooth puree.
In a separate bowl, add heavy cream and whip until stiff peaks form, about 3-4 minutes. Set aside.
In a large mixing bowl, mix cream cheese, sugar, lemon juice, and vanilla extract until evenly combined. Fold in the whipped cream and blackcurrant puree into the cream cheese mixture.
Pour the cheesecake mixture into the prepared crust and smooth out the top with a rubber spatula or offset spatula. Refrigerate to set for 6 hours or overnight, or set in the freezer for 3-4 hours.
Top with fresh blackcurrants, mint leaves, and physalis for garnish (optional).