1. To make the pistachio filling, place the pistachio paste and sieved icing sugar in a bowl and mix to combine.
2. Temper the chocolate by placing it into a saucepan over an induction cooktop on setting 4. Stir continuously until you have 50% solids and 50% liquid. Transfer the chocolate into a heat-proof plastic bowl and stir vigorously until the solids have completely melted.
3. Spread half of the tempered chocolate out to a thickness of 5-7mm over a sheet of baking paper and allow to set at room temperature.
4. Once set, spread the pistachio filling into a thin layer over the chocolate, leaving a small border without filling around the edge of the chocolate.
5. If required, reheat the remaining chocolate with a hairdryer, then spread it over the pistachio filling.
6. Before the top layer of chocolate sets, sprinkle the chopped pistachios and sea salt over the surface.
7. Place into the refrigerator for 5 minutes to set, then break it into pieces.

Note:    Store in an airtight container for up to 10 days.