Preheat oven to 350 degree F. Line a 9×9 pan with butter paper.
Pour melted butter into a huge blending bowl. Whisk in sugar with the help of hand for 30 seconds.
Add in eggs and vanilla extract. Whisk 1 minute.
Whisk in melted chocolate till blended.
Use a rubber spatula to stir in flour, cocoa powder, and salt till simply blended. Stir in all the chocolate chips.
Pour into the prepared pan.
Bake in the preheated oven for half-hour. Let cool in pan 30 minutes before slicing.