To make the base, blitz together all the ingredients and press into the base and sides of a rectangular fluted tart tin. Place into the fridge to harden. Meanwhile, make a jam by placing 150g of the defrosted berries(not any of the juices) into a saucepan with the sugar and boil together for 5 minutes. Remove off the heat and allow to cool down to thicken. When ready, spread 3 tablespoonfuls into the tart case. Next, make the filling. Place the remaining 150g berries into a processor with the maple syrup and lemon zest and blitz. Add in the soaked cashew nuts (discarding the water) and blitz once again till smooth and creamy. Remove the coconut milk from the fridge, open the tin and scoop out just the cream. You will not need the water. Place the cream into a bowl and whip. Also, melt the agar agar in a pan with the lemon juice. Finally, fold the whipped coconut cream and agar mixture into the cashew nut and raspberry filling. Use to fill the prepared tart case, flatten out and place into the freezer for 1 hour to set. When ready, place onto your serving dish and decorate the top with the remaining jam, sliced fresh berries and edible flowers.