Preheat oven to 160C/320F (all oven types).

Spray a 20cm/9" square tin with oil and line with baking/parchment paper with overhang (so it can be lifted out once cooked).

Place biscuits in a food processor and blitz until fine crumbs form. Add butter and sugar and blitz to combine - it should look like wet sand. (Note 1)

Pour into tin and use something with a flat bottom to press into base.

Beat cream cheese until smooth, not fluffy. Add flour and beat until just combined.

Add sour cream, sugar, vanilla and lemon. Beat until combined. Add eggs, one and a time, beating in between until just combined.

Fold in most of the blueberries - reserve some for topping. Pour into tin and smooth surface. Top with remaining blueberries.

Bake for 35 minutes (fan forced / convection) or 40 minutes (standard), or until cheesecake is set but the middle wobbles a bit like jelly - see video. The surface should not be browned, there will probably be some minor cracks.

Cool in tin, then refrigerate (covered) for at least 4 hours. Use paper overhang to lift out, dust with icing sugar if desired. Cut into squares or bars. Serve!