Place the pitted dates and cashews in a small bowl and cover with boiling water; let sit 10 minutes. Drain and pat dry.
Transfer the soaked dates and cashews to a food processor fitted with a steel blade. Pulse in long bursts until a sticky paste forms and only small bits remain, scraping down the bowl as needed.
Add the coconut sugar, vanilla extract, and kosher salt. Pulse to incorporate, then blend until the mixture becomes a fairly smooth dough. If too sticky to handle, chill the dough in the processor for 10–15 minutes.
Line a baking sheet with parchment paper. Use a small scoop or spoon to portion the dough, then roll each portion into a ball with your hands and place on the prepared sheet. You should have 12–15 truffles depending on size. Freeze for 10–15 minutes to firm up.
While the truffles chill, melt the chopped dark chocolate in a heatproof bowl set over a pan of simmering (not boiling) water, making sure the bowl does not touch the water. Stir often until almost melted.
Remove the bowl from the heat, stir in the coconut oil until the chocolate is smooth and glossy.
Remove truffles from the freezer. Working one at a time, dip each truffle fully into the melted chocolate, use two forks to coat and lift it out, then tap away excess chocolate. Place on the parchment-lined sheet and immediately sprinkle with coarse sea salt.
Let the chocolate set at room temperature for a minute or two, then enjoy.