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.
Lightly spray a muffin top pan with cooking spray and set aside. (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 medium cookie scoop, scoop out balls of cookie dough into prepared muffin top pan, leaving plenty of space to spread.
Bake for 14-15 minutes, until lightly golden
When cooked and lightly golden, remove cookies from oven and immediately use a ¼ cup measuring cup (or similar) to press divots into the hot cookies.
Let cool on tray for 5 minutes, before cooling completely on a cake rack