To make the crust: Line a rectangular baking pan with parchment paper. In a food processor, combine the cashews, coconut, dates, and cinnamon. Pulse until finely ground and the mix forms a ball, about 2-3 minutes.
Press the crust mixture into the bottom of the prepared pan, making sure to pack it in tightly. Chill in the fridge.
Combine the coconut cream and honey/maple syrup in a large pot. Set over high heat and bring to a boil. Once boiling, boil for 10 minutes.
Remove from heat and whisk in the lemon juice, vanilla extract, and a pinch of salt. Stir in the chopped white chocolate, if using, until melted and smooth.
Carefully pour the coconut cream mixture onto the chilled crust. Cover and chill for at least 2 hours, or until set.
Before serving, remove the tart from the pan and top generously with fresh mixed berries. Keep chilled until ready to serve.