Preheat your oven to 180 ºC/350 ºF.
Prepare two baking sheets by lining them with baking paper.
Place your flour, sugar, baking powder and cornstarch in a medium mixing bowl and set aside.
In a small saucepan over a medium-low heat, melt your butter.
Stir in your nutella, salt and vanilla extract, allowing just to mix together.
Remove your nutella mixture from the heat and slowly add in your egg white, mixing to combine.
Add your nutella mixture to your flour and stir until just combined.
Stir through your chocolate chips and shape into balls.
Flatten your cookies on your cookie sheet (to about 1cm thickness) and then bake for 7-10 minutes or until the edges are just starting to crisp up.