In a small saucepan, cook the blackberries on medium-high heat until they have released their juices and part of the liquid has evaporated.

Pass the blackberry mixture through a sieve to remove the seeds and skin.

Return the blackberry juices to the saucepan and cook them further until thickened. You want them to be viscous, but not quite jam-like.

Remove from heat and allow to cool completely.

Adjust the oven rack to the middle position, pre-heat the oven to 355ºF (180ºC) and line an 8 inch square baking tin with baking/greaseproof paper.

Mix together the crushed digestive biscuits and melted butter, then press them into the lined baking tin to form a firm, even layer. This is easiest done using the flat bottom of a glass or measuring cup.Depending on the type and brand of cookies/biscuits you use, you might need slightly less or slightly more butter than listed in this recipe. Add the butter slowly, mixing well after each addition, until you reach the consistency of wet sand. You want a mixture that somewhat sticks together or holds its shape when pressed together, but it shouldn't feel/look greasy or oily.

Bake at 355ºF (180ºC) for 10 minutes, then remove from the oven and allow to cool slightly.

Reduce the oven temperature to 285ºF (140ºC).

In a large bowl using a whisk, mix the cream cheese and yoghurt together until smooth. Make sure to MIX rather than whisk or aerate – you don't want to incorporate too much air into the mixture. If you don't want to do this by hand, don't use a hand mixer. Instead, use a stand mixer fitted with the paddle attachment on the lowest speed setting.

Add the sugar and cornstarch, and mix until combined.

Add the eggs, one at a time, mixing well after each addition, until smooth.

Add the lemon juice, vanilla and lemon zest. Mix well until smooth.

Add 1 ½ tablespoons of the base cheesecake filling into the cooled blackberry reduction and mix until evenly combined. Set aside.

Transfer the remaining base cheesecake filling on top of the slightly cooled cheesecake crust, and smooth it out into an even layer.

Gently spoon the blackberry mixture on top of the base cheesecake filling (see post for step-by-step photos) and use a skewer or toothpick to swirl it around.

Evenly distribute the fresh blackberries on top.

Bake at 285ºF (140ºC) for about 30-35 minutes, or until the filling is very light golden brown around the edges and the middle is still slightly wobbly when you shake the baking tin.

Turn off the oven and allow the cheesecake bars to cool to room temperature in the turned-off oven with the oven door ajar.

Once cooled to room temperature, transfer the cheesecake bars into the fridge for at least 1 hour (or preferably overnight) before removing them from the baking tin and serving.

The blackberry cheesecake bars keep well in a closed container in the fridge for 3 - 4 days.