Put dates and boiling water in a cup for 2 minutes to soften.
Combine with all other base ingredients into food processor and process until a clumpy texture. Do not over process. It should have some small pieces of cashews showing. You may need to add a little more water if it is too dry.
With a rubber spatula, press the base into 25cm (10in) tart dish (the ones with removable bottoms are best). Make sure you get a thick crust along the sides.
Soak filling dates in boiling water for 2 minutes and combine with all other filling ingredients in a food processor. Process until you have a very smooth cashew cream.
Pour out over the base and make level.
To make the topping, mix arrowroot, lemon juice and water in a cold small pot or frying pan.
Add blueberries and start heat (stirring well) until a gel has formed.
Pour blueberry topping over the cheesecake to complete. Use a fork to evenly distribute.
Refrigerate covered for several hours to help it firm up so it is easier to serve.