Preheat your oven to 170C / 340F. Line two baking trays with baking paper.
Add the caster sugar, brown sugar, egg, butter and vanilla extract to a large bowl and use an electric hand mixer to beat until pale and creamy, about 3 minutes.
Add the all-purpose flour, bicarb soda, salt, rolled oats and chocolate chips and mix using a spatula until a dough forms. Chill the dough in the fridge for 1 hour for chewier cookies with an even spread.
Use a medium sized cookie scoop to scoop rounds of the cookies onto the baking tray and bake for 12 minutes or until golden around the edges. Add some extra chocolate chips on top if you wish and allow to cool before serving or serve warm.