Preheat the oven to 190ºc/170ºc fan and line 2-3 large trays with parchment paper.
Add the banana to a bowl and mash, and then add the butter and sugar and mix.
Add in the egg yolk and vanilla and beat again.
Add in the plain flour, bicarbonate of soda, salt and cinnamon and beat.
Add the chocolate chips and mix through.
Use a 5cm scoop to portion the cookies onto the trays.
Bake the cookies in the oven for 10-12 minutes and leave to cool for 30 minutes at least to set.
