Preheat your oven to 160°C/320°F (or 140°C/285°F for fan/convection ovens). Line an 8x8-inch tin with baking paper.
In a large bowl, mix the melted butter, caster sugar and light brown sugar together. Then stir in the eggs and vanilla extract.
Add the flour and mix well to make a smooth blondie batter.
Fold in the Rolos and the chocolate chips. Save a few for topping if you like.
Transfer the batter to your lined tin and spread it out evenly. Bake for around 35 minutes, until they're golden brown and pulling away from the tin slightly.
Leave the blondies in the tin to cool completely then put them in the fridge for 3-4 hours to set. This will make the gooey centre turn firm and fudgy.
Once set, cut into squares and enjoy!