Grease a line a 20 x 30cm (8 x 12") slice tin, leaving extra parchment overhanging to help you remove the slice from the tin, and set aside.
Crush biscuits (250 g) into a fine crumb using a food processor (or place them in a plastic bag and give them a bash with a rolling pin), and place into a bowl.
Then add condensed milk (250 g/¾ cup), melted butter (80 g), lemon juice & zest (from 1 lemon - approx ¼ cup of juice), roughly chopped dried blueberries (70 g/½ cup) and desiccated coconut (45 g/½ cup) to the biscuit crumbs and mix well to combine.
Press mixture into the lined tin and even out the surface, then set aside.
Place the white chocolate (225 g) and vegetable oil (2 tbsp) in a small microwave-safe bowl and melt in the microwave in 30 second bursts (mixing with a metal spoon in between bursts) until just melted, then mix well to combine the oil and chocolate.
Pour the melted white chocolate on top of the lemon biscuit base, tilting to spread evenly. Sprinkle extra coconut on top and place in the fridge for 1-2 hours, or until set.