Place the butter, light brown sugar and caster sugar into a large mixing bowl and whisk till light, creamy and fluffy.
Add an egg and vanilla extract into the mixing bowl and whisk together until combined.
Add the plain flour, baking powder and bicarbonate of soda into the mixing bowl and whisk until a cookie dough has formed.
Pour the milk chocolate chips, dark chocolate chips and white chocolate chips into a mixing bowl and whisk until evenly distributed within the dough.
Separate the dough into 8 equally sized sections, they should be around 115g to 117g each. Then, with your hands roll each chunk of dough into a ball and place on a plate or baking tray.
Place in the freezer for 30 minutes for the dough to firm up.
Whilst the cookies are freezing, preheat your oven to 200°C (gas mark 6, 400°F) and line a baking tray with parchment paper.
Place the cookie dough balls into a lined baking tray and bake in the oven for 14 minutes. Once baked, leave the cookies to cool for at least 20 minutes before eating.