Preheat the oven to 140°C fan / 160°C / 320°F.
Add the gluten-free digestive biscuits to a food processor and blitz into crumbs. You want fairly fine crumbs, but avoiding blitzing them into dust!
Transfer the biscuit crumbs to a mixing bowl, pour in the melted butter and mix until everything is well combined.
Spoon the mixture into a 20cm (8in) loose-bottomed or springform tin and firmly compact it into an even layer.
Bake for 10 minutes, then remove from the oven and allow to cool slightly whilst you make the filling. Keep the oven at 140°C fan / 160°C.
Fit a stand mixer with the paddle/beater attachment.
Add the cream cheese and mix on a low speed for around 1 minute, just until smooth.
In a small bowl, mix together the flour, caster sugar and salt. Gradually add this to the cream cheese, mixing on a low speed only until combined.
Add the eggs one at a time, mixing briefly after each addition.
Add the vanilla extract, lemon zest and lemon juice and mix again just until incorporated.
Turn the mixer off and fold in the sour cream by hand until evenly combined. It should be like the texture of custard that drizzles off of a spatula.
Pour around half of the cheesecake filling over the pre-baked biscuit base, then scatter over HALF of the blueberries for the cheesecake.
Pour over the remaining cheesecake filling and scatter over the remaining blueberries. Gently press any blueberries sitting right on the surface just beneath the filling.
Bake for around 55-60 minutes. The cheesecake is ready when the outer few centimetres are set but the centre still has a gentle wobble when the tin is lightly shaken. The middle shouldn’t look liquid and the top should remain fairly pale.
Turn the oven off and immediately leave the oven door ajar by around 10–20cm. Leave the cheesecake inside the switched-off oven for around 1 hour.
Remove from the oven and leave at room temperature until completely cool.
Cover and refrigerate for at least 6 hours, ideally overnight.