Place a sheet of parchment paper on a small baking sheet (about 33x22 cm).
Put the chocolate pieces in a medium glass bowl.
Add cupful of water to a small medium saucepan, then bring to a boil. Place the glass bowl with the chocolate on top of the saucepan - its base should not touch the water.
Stir the chocolate with a spatula as it starts to melt. When it has melted, pour it onto the baking sheet, spreading it out evenly with the spatula. Sprinkle with some course sea salt and the pistachio.
Place the baking sheet in the fridge for about an hour, until solid.
Let it come to room temperature, then cut it into squares or snap it into uneven pieces.
Keep the shards or squares in an airtight jar.