Heat the oven 200C/180C fan/Gas mark 6. Weigh out the vegetable spread; break up 200g of the chocolate, placing both ingredients into a small saucepan, and cook over a low/medium heat. Once melted completely, sift in the cocoa powder and mix together with a spatula until smooth and shiny. Put in the fridge to chill.
In a large mixing bowl, use an electric mixer to combine the sugar and the eggs. Once the mixture thickens to a pale, custard like colour; remove the chocolate from the fridge and fold in, ensuring you have a lovely chocolatey colour all the way through the mixture.
Next, combine the flour by folding through. Pour the batter into a tin, lined with greaseproof paper. Drizzle the peanut butter all over the top of the batter, using a fork to make swirl effects throughout
Take the bananas and cut length ways, about ½ cm thick. Lay the banana strips over the top of the peanut butter, covering the brownie
Cut up the remaining dark chocolate, roughly scattering it over the top of the banana, poking some pieces into the batter itself
Transfer to the middle shelf of the oven and bake for 35 minutes. The middle should still have a slight wobble if shaken gently. Remove from the oven and leave to cool down, before removing from the tin and transferring to the fridge to chill before serving