Preheat the oven to 180°C and line a pan for the brownies.
Melt the butter over a low heat in a large saucepan. Whisk in the treacle and sugar and then set aside for a moment.
In another bowl, sieve together the flour and cocoa.
Return to the melted butter and beat in each egg individually before folding in the flour.
Pour the mixture into the lined pan, sprinkle over the sea salt and bake for 25-35 minutes.
The top should be just dried out but the mixture underneath still slightly damp, as the brownies will set a little more as they cool. Once they’re done, let the brownies cool in the pan for 30 minutes before removing and cutting into squares.