Line a baking tray (approximately 20 × 30 cm) with baking parchment.

Place the chopped dark chocolate in a heatproof bowl. Set it over a pan of gently simmering water, ensuring the bowl does not touch the water. Stir occasionally until fully melted.

Remove the bowl from the heat and allow the chocolate to cool slightly for 2–3 minutes.

Stir in two-thirds of the chopped pistachios.

Pour the chocolate mixture onto the prepared tray and spread it evenly using a spatula to about 5 mm thickness.

Sprinkle the remaining pistachios over the surface and gently press them into the chocolate. If using, scatter the sea salt flakes on top.

Place the tray in the refrigerator and chill for at least 1 hour or until fully set.

Once set, break the bark into shards using your hands or cut with a sharp knife.

Store in an airtight container in a cool place for up to one week.