Preheat your oven to 180°C/350°F (160℃/320℉ for fan and convection ovens). Line a large baking tray or two with baking paper.
Cream the butter together with the caster sugar and brown sugar. Then stir in the egg and vanilla extract.
Add all of the flour and the Rice Krispies and mix well. When it's starting to stick together, use your hands to press it all together into a ball of dough.
Add the chocolate chips and gently work them into the dough with your hands.
Divide the dough into 12 equal-sized pieces and roll them into balls.
Place them onto your baking tray, leaving a couple of inches in between to allow for spreading. Usually bake 4-5 at a time.
Bake for 11-12 minutes, until the cookies are lightly golden at the edges. They will look a bit underbaked at first but will become more golden as they cool.
Let them cool completely on the tray then enjoy!