Start by lining up the pitted dates on a parchment paper. You want to lay them down open (see image) and form a square, 5 dates down by 5 dates to the side.
Place another piece of parchment over the dates and with the help of a rolling pin, flatten down until you have a layer of mushed together dates. Don't worry if there are some holes, it doesn't need to be a perfectly full layer.
Remove the top parchment paper and spread a layer of nut butter. It helps if the nut butter is soft. If yours is hard try warming it up for a few seconds in the microwave first - remember to remove the foil top!
Sprinkle with pistachios and walnuts. You can freeze the bark at this point and proceed later or continue now (it all depends on how runny your butter is).
Melt the chocolate chips and stir in the coconut oil (the coconut oil helps render the chocolate more smooth and creamy but can be skipped if that's what you prefer). Pour the melted chocolate over the bark. Smooth with an offset spatula or a spoon. Immediately top with the coconut and sea salt flakes. Freeze until firm.
Once firm, remove from the freezer and cut into pieces. Place in a resealable container and keep in the freezer until ready to eat.