Preheat your oven to 180°C and line a baking sheet with parchment paper.
In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the egg and vanilla extract until well combined.
In a separate bowl, whisk together the self-raising flour, baking soda, and salt.
Gradually add the dry ingredients to the butter mixture, mixing until just combined.
Fold in the milk chocolate chips (or chunks).
Divide the dough into 6 equal portions and form large cookie dough balls. Place them on the prepared baking sheet, leaving space between them to spread.
Place in the fridge for 30 minutes before baking.
Bake for 10-12 minutes until the edges are set but the centres are still soft. The cookies will continue to bake on the sheet as they cool.
Allow the cookies to cool on the baking sheet for about 10 minutes before transferring to a wire rack.