Preheat oven to 350°F. Lightly grease a light-colored 8x8-inch metal pan with cooking spray. Line with parchment paper, leaving an overhang for easy removal. (Avoid foil or wax paper.)
In a large mixing bowl, whisk together melted butter, granulated sugar, and brown sugar until the sugar dissolves. Add eggs and vanilla, whisking until smooth and creamy.
Add flour, cocoa powder, and salt to the bowl. Switch to a wooden spoon and mix until just combined. Stir in ½ cup mini chocolate chips—do not overmix.
Scrape the batter into the prepared pan and smooth the top. Sprinkle the remaining ¼ cup mini chocolate chips evenly over the surface.
Bake on the middle rack for 25 to 30 minutes, or until the brownies are just set to the touch. Do not overbake; they will firm up as they cool. The centers are meant to be fudgy and gooey!
Let brownies cool completely. Using the parchment overhang, lift them from the pan. Cut into squares using a sharp knife. For clean cuts, run the knife under warm water, wipe dry, and repeat between cuts. Sprinkle with flaky sea salt if desired. Enjoy!
