Preheat the oven to 200C/180C Fan/Gas 6. Place the rhubarb, grapefruit juice, sugar and star anise onto a baking tray and cook for 5–10 minutes, or until soft but keeping its shape. Set aside and discard the star anise – but keep any cooking syrup.
For the base, crush the biscuits until you have crumbs, either by using a machine or by hand with a rolling pin. Add the melted butter and stir. Press them into the bottom of a 20cm/8in springform cake tin. Set in the fridge for at least 1 hour.
Meanwhile, make the filling. Tip all the ingredients into a large bowl and whisk to combine. Pour on top of the set biscuit base and set in the fridge for at least 1 hour.
To assemble, top the set cheesecake with the poached rhubarb, then decorate with the syrup, ginger biscuit crumbs and fresh mint sprigs.
