Slice the dates open like a book to remove the seed. Stuff each date with 1/2 - 1 teaspoon nut butter (or as much as they will fit). Close the dates and place them on a small lined plate and into the freezer.
Melt the chocolate and cacao butter in a small bowl. You can do this as a double boiler or in increments in the microwave.
Once the chocolate is melted and smooth, use two forks to dip each date into the chocolate and coat is completely. Rest the date on one fork to allow excess chocolate to drip off. Repeat with the remaining dates - you will have just enough chocolate for one coating on each date (no waste here!)
The dates should start to set quite quickly. As they do, sprinkle over a pinch of sea salt, if you're using it. You could also use some crushed nuts.
Place the dates in the fridge to set. I recommend keeping them in the fridge in an airtight container - the chocolate isn't tempered, so it will melt as it warms.