Pre-heat oven to 180c.
Grease and line a 20cm/8" square (base measurement) cake tin and set aside.
In a medium-sized bowl, combine the salted butter and the golden caster sugar and using a hand-held mixer, mix until fluffy.
75 g salted butter, 100 g golden/raw caster sugar
Add eggs and vanilla essence, mixing until combined.
2 eggs, 2 teaspoon vanilla essence
Add Nutella and mix well until combined.
330 g Nutella
Add plain flour and mix by hand until just combined. Don't overmix.
120 g plain flour
Fold in chocolate chips and peanut butter chips, then pour batter into the prepared tin.
70 g milk chocolate chips, 70 g peanut butter chips
In a small bowl, combine the peanut butter and the remaining Nutella, then place dollops of this mixture evenly on top of the batter mixture. Take a knife and gently swirl the peanut butter mixture to combine slightly (see photos above) and bake for 34 mins (see notes).
2 tablespoon smooth peanut butter