Heat oven to 200C/180C fan/gas 6.
Line a 20 x 30cm rectangular tin with
baking parchment. Put the biscuits in a
food processor and blitz to a fine crumb.
Add the butter and blitz again to combine.
Tip into the tin, press down firmly with
the back of a spoon to cover the base,
then bake for 10 mins. Leave to cool.
Meanwhile, tip 25g of the sugar and the
blueberries into a small pan. Mix the
cornflour with 1 tbsp cold water and add
this to the pan. Heat gently until the sugar
dissolves. Increase the heat and bubble
for 1-2 mins until saucy. Set aside to cool.
In a large bowl, whisk the cream
cheese with an electric hand-held whisk
until smooth. Add the remaining sugar
and whisk again. Add the flour, vanilla,
eggs and soured cream, and whisk until
smooth and well combined.
Pour half the cheesecake mixture over
the biscuit base, then spoon half the
blueberry sauce on top in small blobs.
Cover with the remaining cheesecake
mix and smooth the surface with a
spatula. Drizzle the remaining blueberry
sauce over the top, then use the end
of the spoon to ripple it into the
cheesecake. Bake for 10 mins, then
lower the heat to 110C/90C fan/ gas ¼
and bake for a further 30 mins. Turn off
the oven and leave the cheesecake inside
for 1 hr, then leave for 1 hr more with
the door ajar. Finally, leave at room
temperature until completely cool, then
chill for at least 3 hrs or, even better,
overnight. Slice into 14 bars. Will keep
in the fridge for up to 5 days.