Preheat the oven to 350°F. Grease an 11‑inch round tart pan with coconut oil.
To make the crust, place the hazelnut meal, arrowroot powder, coconut sugar, and sea salt into a bowl and mix together.
Add the coconut oil and mix it in, using your fingers or a pastry cutter, until fine crumbs form.
Add the water and stir together with a wooden spoon until the mixture forms a ball. Press the dough into the bottom and up the sides of the tart pan.
Bake the tart for about 25 minutes, then remove from the oven and cool completely. I like to put it into the refrigerator to speed up the cooling process.
To make the filling, place the cashews into a bowl of water and let soak for about 3 hours; then drain and rinse.
Place soaked cashews into a high-powered blender, add the cacao powder, maple syrup, coconut milk, and vanilla and blend until super smooth, adding more coconut milk by the tablespoonful if needed.
To assemble the tart, pour the chocolate filling into the cooled crust and chill for 2 hours.
Pop the tart out of the pan by pushing it up from the bottom.
Transfer to a serving platter. Decorate the top with the raspberries and serve.