Preheat the oven to 350 degrees and line 7×11, 8×8, or 9×9 in baking pan with parchment paper. Crumble up the parchment paper before lining the pan. Melt the butter in the microwave and let it cool slightly. Then, mix it with the eggs, sugar, and vanilla in a stand or hand mixer with the paddle attachment. Add the cocoa powder and continue mixing until combined. Add the flour and salt to the mixture and mix again. Add 1 1/2 cups of the chocolate chunks into the batter and stir to combine. Spread out the batter into the prepared baking pan. Scatter the remaining chocolate chunks to the top of the batter. Bake for 24 to 30 minutes or until the edges are just set and a toothpick inserted into the center comes out with a few moist crumbs but no thick batter. Try not to over bake. Cool the brownies in the pan on a wire rack for at least 30 minutes to an hour until set and cool. Cut into 8 rectangles just like Starbucks brownies and enjoy!