Preheat the oven to 180°C. Line a few trays with baking paper. I use 3 for this recipe as the cookies spread so much.
Cream together the butter and sugars until light and fluffy.
Add the egg and vanilla extract stir in well.
Sieve in the flour and salt and mix into a dough.
Pop in the fridge for 1 hour.
Remove from fridge and take a heaped tablespoon for each cookie. Roll into a ball and flatten into a disc. Put a heaped teaspoon of peanut butter in the centre of the disc and the banana. Roll the cookie back into a ball by pulling the sides in. Put on a baking tray, leaving a good distance between them as they will spread.
Bake for 10-12 mins until the cookies are starting to brown.
Leave to cool slightly before enjoying.