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, vanilla extract and salt.
Add all of the flour and mix well to make a smooth blondie batter then fold in the chocolate chips.
Transfer the batter to your lined tin and spread out evenly. Drizzle the peanut butter and Nutella on top then use a toothpick to swirl it around to make a pattern.
Bake for around 35-40 minutes, until the edges look firm and are pulling away from the tin slightly. The middle should 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!