Place the digestive biscuits and 15g sugar in a freezer bag. Crush finely with a rolling pin.
Melt the butter and pour it into the bag. Massage until well combined.
Press the mixture firmly and evenly into the bottom and up the sides of a tart tin (about 22 cm / 9 inches Ø).
Bake the crust at 180°C/355°F (conventional oven) for 8 minutes, until just golden. Let cool completely.
Prepare the filling
In a bowl, whisk cream cheese, powdered sugar, vanilla sugar, and lemon zest until smooth and fluffy.
Whip the heavy cream to soft peaks in a separate bowl.
Gently fold the whipped cream into the cream cheese mixture, a little at a time.
Spread the cream filling evenly over the cooled crust. Smooth the top. Chill for at least 1 hour.
Prepare the blueberry compote
Add blueberries, water, and 75g sugar to a saucepan. Bring to a boil, then simmer for 5 minutes.
Mix the potato starch with a splash of cold water, then stir into the blueberries while heating. Bring just to a boil to thicken, then remove from heat.
Cool the compote slightly. Spread gently over the cheesecake. Refrigerate until set, at least 2 hours or overnight for best results.
Keep the display on
Notes
For best results, chill the cheesecake overnight to allow the flavours to meld and the texture to set.