Place all the 'melting' ingredients (except the peanut butter) together in a heatproof bowl. Place over a saucepan with boiling water and melt slowly to avoid splitting. Once the mix has melted, stir in the peanut butter and heat through for a few minutes until fully incorporated. Leave the mix to cool to room temperature.
Sieve the flour and cocoa powder together into a bowl, add in the salt. Keep the sieve for later.
Preheat oven to 160C Fan/180C Conventional
Now start whisking the chickpea water using an electric whisk. Whisk for about 10 minutes, until you start to see stiff peaks forming (as if you were making meringue). Test that the mix is semi-solid and won't fall on your head if you tip it upside down!
Once stiff, start whisking in the sugar one spoonful at a time so that it slowly incorporates and maintains its firmness. It should end up looking shiny and stiff.
Once the chocolate mixture is cool, fold it into the chickpea mix using a large metal spoon. Make sure you don't beat any of the air out! What you should end up with is a chocolate mousse substance.
Sieve the flour mixture into the mousse and fold this in until it's just about incorporated.
Fold in the walnuts and date pieces until combined.
Pour the mix into a greaseproof paper-lined tin and carefully push the mix so it fills the whole tin evenly
Bake in the oven for 25 minutes. Check that there is a crisp layer on the top of the brownie and that it only wobbles slightly. If not, put it back in for another 5/10 minutes. You can put foil over the top to make sure it doesn't burn.
Let it cool down/scoff it down as soon as it's cool enough to eat...maybe add vegan vanilla ice cream and pretend like you were supposed to eat it warm!