Preheat the oven to 350°F/180°C. Grease an 8x8 inch square baking pan. Option here to line the pan with aluminum foil before greasing to help lift the brownies out at the end.
Place the chocolate chips or chunks in a microwaveable bowl and sprinkle all of the chopped up butter on top. Microwave them for 30 seconds, stir, and then microwave again for 20-30 seconds until the chocolate is melted. Then add the cocoa powder and 2 tbsp of oil and continue stirring until the cocoa powder has dissolved and blended into the mixture. Set this aside to cool while you prepare the remaining ingredients.
In the bowl of a stand mixer fitted with the paddle attachment, add the two sugars, eggs, and vanilla. Beat them on medium to medium-high for 6-7 minutes, until pale yellow in color and ribbony. Make sure to beat them for this full length of time and no shorter! Then, fold in the melted chocolate mixture and beat for another minute.
Add the flour and salt. Use a flexible spatula to fold these ingredients in until combined. At this point, also fold in additional chocolate chips. Transfer the batter to your prepared baking pan, spreading it into an even layer.
Bake for 25-30 minutes, or until the edges look crisp and middle is set. When in doubt, it is better to underbake than overbake brownies.
Let them cool completely before cutting into 16 equal pieces. Optional: sprinkle with flaky sea salt. Enjoy!