Pre heat your oven to 180C / 350F / Gas mark 4. Grease or line your 1-pound loaf tin and put it to one side.
Melt the chocolate either in a microwave on half power for 30 seconds at a time or in a double boiler, once melted put aside for the moment to cool slightly.
Cream the butter and sugar together until light and fluffy.
Add the eggs one at a time mixing in between each addition.
Add the flour, baking powder and cocoa, melted chocolate and mashed banana.
And stir gently to bring it all together.
Pour it into your prepared loaf tin and smooth the top out.
Place in the oven and bake for 50 to 55 minutes until its firm to the touch and a skewer comes out clean.
Allow to cool in its tin for 10 minutes then transfer it to a cooling rack. Once fully cool, serve.