In a small saucepan bring heavy cream to 120ºF/50ºC. Turn off the heat.
Add butter and chopped dark chocolate and stir until all melted. Add a pinch salt and stir until combined.
Coat 9cm x 15cm (or 12cm x 12cm) pan with parchment paper, add chocolate mixture. Refrigerate for 3 hours.
Take out the nama chocolate from fridge and cut into about 2.5cm x 2.5cm square with hot knife. Clean the knife with hot towel every cut.
Dust with cocoa powder.
Nama Chocolate is ready to serve.