Grease a 18cm tart tin. Set aside. In a food processor combine dates, almonds, cashews and salt, process until nuts grounded and combined. Firmly press the mixture into the bottom and sides of the prepared tart tin. Place in the freezer to set while you work with your filling.
In a blender, add blackberries and lemon, puree until smooth. Add blackberry puree, maple syrup, coconut milk, into a saucepan and cook on a medium-high heat, when the mixture started to boil, add cornstarch and agar-agar, constant stirring until agar completely dissolved.
Strain mixture through a mesh sieve.( you can skip this step, but straining will result in a finer texture). Pour mixture to a cooled tart and place in the fridge for 1 hour t to set.
Make the jelly, add blackberries in a blender and puree until smooth. Strain through a mesh sieve.
In a saucepan, add water, blackberry puree, maple syrup. Bring to a boil, whisk in the agar powder. Let it simmer for 3 minutes, until agar is completely dissolved. Stirring constantly
Turn off the heat and allow mixture to cool to room temperature before gently pouring over the top of the set blackberry custard. Place tart in the fridge for 2 hours to set. Remove tart from the tart tin and garnish with berries. Enjoy!