Preheat the oven to 150 celsius (300 Fahrenheit) and line a [amazon_link id="B000G0KJG4" target="_blank" ]baking tray/sheet[/amazon_link] with baking paper. Add the cocoa powder and spread it into an even layer and roast for 2 hours, stirring every 20 minutes to ensure it doesn't catch and burn. Leave to cool completely before making the cake.
Grease a 20cm (7 inch) springform pan and preheat the oven to 180 Celsius (350 Fahrenheit).
Place the ingredients in the bowl of a food processor and process until smooth. Pour the batter into the springform pan and bake for 35 to 50 minutes. Check the cake after 30 minutes as you may need to cover it with foil to prevent burning before the cake is cooked through. Remove from the oven and let the cake cool completely in the tin before removing.
To make the glaze place the cream in a small saucepan and bring to a boil over a medium heat. Remove from the heat and add the chocolate and leave to sit for a minute. Add the sea salt and whisk to combine. Leave to cool at room temperature until the glaze is a spreadable consistency and not too runny. Spread the glaze across the top of the cake and ease it down the sides with an offset spatula.
I always find chocolate cakes taste better the next day, so I would suggest making this the day before you intend to serve it.