Make the blueberry compote. Place the blueberries, 2 tablespoons of granulated sugar, and the lemon juice in a small saucepan over a medium heat. As the berries warm, you'll hear a soft sizzle, then see them begin to burst and release their deep purple juices. Let it bubble gently for 5-6 minutes. Stir in the cornflour slurry and cook for another minute until the mixture thickens to a glossy, jam-like consistency. You should be able to drag a spoon across the bottom of the pan and see the trail hold for a second. Remove from the heat and let it cool completely.

Prepare the biscuit base. Place the digestive biscuits in a sturdy freezer bag and crush them with a rolling pin until you have a mix of fine crumbs and a few slightly larger, pebble-like pieces for texture. You want the sound to be a satisfying crunch, not a powder. Tip the crumbs into a bowl, add the melted butter, brown sugar, and cinnamon, and stir with a fork until the mixture looks like wet sand and clumps together when squeezed.

Press the base into the tin. Line a 20cm (8-inch) square baking tin with parchment paper, leaving an overhang on two sides for easy lifting. Tip the biscuit mixture in and press it down firmly and evenly using the flat bottom of a glass or a measuring cup. The base should feel compact and solid, not crumbly. Place the tin in the fridge to firm up while you make the filling.

Whip the cream. In a large, clean bowl, pour in the very cold double cream. Using a hand mixer or stand mixer, whip the cream on medium-high speed until it forms soft peaks. You'll know it's ready when it holds its shape gently on the whisk and looks pillowy and white. Be careful not to over-whip, or it will turn buttery.

Beat the cream cheese filling. In a separate large bowl, beat the softened cream cheese with the caster sugar and vanilla paste until it is completely smooth, glossy, and free of any lumps. The mixture should smell sweet and creamy. Gently fold the whipped cream into the cream cheese mixture using a rubber spatula. Fold slowly, turning the bowl, until no white streaks remain and the filling is a uniform, airy cloud.

Assemble the bars. Spread half of the cheesecake filling evenly over the chilled biscuit base. Dollop half of the cooled blueberry compote over the filling in small spoonfuls. Gently spread the remaining cheesecake filling on top, then finish with the rest of the blueberry compote. Use a knife or skewer to swirl the compote into the top layer of cheesecake, creating gentle figure-eight patterns. The surface should look marbled.

Chill and set. Cover the tin with cling film and refrigerate for at least 4 hours, but ideally overnight. The bars need this time to set firm enough to slice cleanly. You'll know they're ready when the top feels set to the touch and the sides have pulled away slightly from the parchment.

Slice and serve. Lift the block out of the tin using the parchment overhang. Place it on a chopping board and use a large, sharp knife to slice into 12 even bars. Wipe the knife clean between cuts for the neatest edges. The bars should have a clean, sharp line when you cut them.