Preheat oven to 180°C/350℉ (or 160°C/320℉ for fan ovens and convection ovens) and line a large tray or two with baking paper.
Add the butter to a large bowl with the caster sugar and brown sugar. Mix to make a thick paste, using an electric whisk or stand mixer if needed.
Add the egg and vanilla extract and mix again to make a smooth mixture.
Mix in all of the self-raising flour. When it's starting to stick together, use your hands to press it into a ball of dough. If the dough is too sticky, add more flour. If it's too dry, add a splash of milk.
Add the chocolate chips and the Munchies and gently knead them into the dough using your hands.
Divide the dough into 12 equal-sized pieces and roll into balls. Make sure that the Munchies are not sitting right at the edges of the balls- try to keep them in the centre to avoid caramel spilling out.
Place the balls of cookie dough on the tray with a couple of inches in between to allow for spreading (around 4-6 per tray).
Bake 11-12 minutes until the cookies are JUST turning golden brown at the edges. They will look underdone at first but just trust the process!
Allow the cookies to cool completely before gently peeling them off of the tray.