Preheat your oven to 160℃ (140℃ if you're using a fan oven). Line an 8x8-inch tin with baking paper.
In a large bowl, mix together the melted butter, caster sugar and light brown sugar.
Stir in the eggs and vanilla extract.
Add all of the flour and mix well to make a smooth, thick blondie batter.
Fold in the Kinder chocolate, Kinder Bueno pieces and the chocolate chips.
Transfer the batter to your lined tin and spread out evenly. Bake for 35-40 minutes, until the edges look firm and are pulling away from the tin slightly. The middle should look baked but still have a slight wobble.
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!