Heat oven to 180°C/350°F/165°FF
Heat butter in microwave until it's just melted. Set aside while you prep the other ingredients.
Line 4 baking trays with baking paper. See notes
Sift the flour, bi carb soda, baking powder and salt together. Set aside
In the bowl of a stand mixer, combine the cooled melted butter and sugars until well blended
Add the egg, egg yolk and vanilla and beat until light and creamy. Beat on medium-high for 5 minutes.
Stop the mixer, add the flour mixture and beat until almost combined
Remove bowl from stand, add chocolate chips, then combine with a wooden spoon or spatula. DO NOT OVERMIX
Using a large ice-cream scoop, scoop out balls of cookie dough onto prepared baking sheet, leaving plenty of space to spread.
Optional: use the extra chocolate chips to push into the top of the dough balls for extra chocolatey goodness!
Bake for 12-14 minutes, until lightly golden
When cooked and lightly golden, remove cookies from oven.
Let cool on tray for 5 minutes, before cooling completely on a cake rack