To make the crust, grind oats in a food processor fitted with the S blade till powder. Add walnuts and grind till they're quite crumbly. Add sea salt and 3 tbsp cacao and pulse to combine.
Add the dates to the processor and process till mixture is sticking together. Add 1 tbsp maple syrup and continue to process till mixture is holding together really well.
Press crust into your tartelette pans, making sure to keep the thickness even and get the sides nice and high. Refrigerate for one hour or more (up to a day or two).
In a high speed blender, blend the cashews, oil, 1/3 cup maple syrup, 1/3 cup cacao or cocoa powder, vanilla, water, and a pinch of sea salt. Let it blend for as long as necessary to make it completely, silky smooth.
Pour the filling into the tartelette shells. Refrigerate for several hours before serving, to let the ganache set. Top with fresh raspberries if desired!
Makes 2 4.75-inch tartelettes, with a little extra left over.