Line an 8 or 9" square baking dish with parchment paper and set aside.
Add the pitted dates and raw cashews to a medium bowl and cover with hot water. Let them sit for at least 10 minutes, or up to 2 hours to get soft.
Rinse, drain, and transfer to the food processor.
Add the melted coconut oil and cacao powder, and pulse until super smooth (scraping down the sides of the food processor as needed).
Pour the fudge into the lined baking dish, smoothing over the top. Top with chopped nuts & coarse salt if using.
Transfer to the freezer until set, about 1 hour. Slice into squares.
To serve: remove from the freezer for a few minutes before serving, or until just soft. Store leftover fudge in the freezer.