Banana, oat and choc chip cookies: Blitz the oats in a food processor for 5-10 seconds, until roughly chopped. Mash the bananas in a mixing bowl, then add the oats and chocolate chips. Mix well then drop large spoonfuls of the mixture onto a lined baking sheet. Cook for 12 minutes. Leave on the tray for 5 minutes then remove to a wire rack to cool.
Peanut butter cookies: Put the peanut butter, caster sugar and egg into a mixing bowl and stir together. Scoop out 1 tablespoon of the mixture and roll into a ball. Place on a lined baking sheet and repeat with the rest. Press each down with a fork then place into the fridge for 30 minutes.
Preheat oven to 180/160C. Bake for 18 mins. Leave on the tray for 5 minutes then remove to a wire rack to cool.
Brownie box-mix cookies: Preheat oven to 180/160C. Put the brownie mixture, egg into a mixing bowl and mix well. Pour in enough butter to bring it all together into a thick paste. Scoop balls onto lined baking sheet and bake for 12 minutes. Leave on the tray for 5 minutes then remove to a wire rack to cool.
Shortbread: Beat the butter and 45 grams sugar together. Stir in the flour then turn onto a lined baking sheet and shape into a 1.5 centimetre thick circle. Cut into 8 segments, prick with a fork and sprinkle with remaining teaspoon of caster sugar. Place in the fridge for 20 minutes then bake for 22-25 minutes until starting to colour around the edges and the centre has firmed up. Slice through again and leave on the tray for 5 minutes before removing to a wire rack to cool.