In a medium saucepan, combine the 2 cups chocolate chips and butter. Cook over medium-low heat, stirring constantly, until melted and smooth. Be careful not to overcook. You will have a soft ball of chocolate in the pan when it is ready. This only takes a few minutes.
Preheat the oven to 350 degrees F and line baking sheets with parchment paper. Using a stand mixer fitted with the paddle attachment (or a large mixing bowl with a hand mixer), combine the sugar, eggs and vanilla extract and beat on medium speed until free of lumps.
In a separate bowl, combine the flour, baking powder and salt. Mix well. Gradually add to the butter-sugar mixture and beat on medium speed until just combined. Add the chocolate mixture from the saucepan and mix on med-high speed for 1 minute. Batter will be light and mildly runny. Stir in the 2 cups chocolate chunks (or chips).
Using a medium cookie scoop, place 1.5-tablespoon-size globs of batter 2 inches apart on the prepared baking sheets. Bake in the preheated oven for 8-10 minutes. Let cool.