The day before: Soak the raw cashews (for the filling) in enough water to cover and set aside the in fridge.
Preheat the oven to 180°C (355°F). Line the base of a 25cm (10-inch) tart pan.
To make the crust: Add all the ingredients to a bowl or food processor and mix until evenly combined and it forms a dough. The dough should be soft but pliable and can be pinched between two fingers without breaking.
Dust a clean surface with flour. Use a rolling pin to roll out the pastry to about ½ cm (¼ inch) thick. Carefully use a rolling pin to transfer the dough to the tin. Press the dough against the bottom and sides of the tin to form a crust.
Bake the crust for 15 minutes or until the surface is evenly golden brown. Set aside to cool.
To make the filling: Drain the cashews and add them to a high-powered blender with the coconut cream, sweetener, vanilla, cacao butter and 1 yellow nectarine (without the stone). Blend until it's as smooth as possible.
Pour the mixture into the tart tin and smooth the top. Place the tart in an airtight container and set in the fridge for 4 hours.
Decorate the tart with the remaining nectarines or as desired and enjoy. Store leftovers in an airtight container for up to 3 days.