• Preheat the oven to 350 F (180 C) for conventional oven, 330 F (165 C) for convection oven. Line a 8 x 8 inch square pan with aluminum foil, overlapping, so all four sides are covered. Brush the foil with a bit of oil or use a cooking spray to prevent sticking
  

Cook the potatoes:

• You can cook 1 or 2 large potatoes, about (250-350 grams or 8-10 oz each). Peel the skin and cut into large chunks.
• Bring a pot of water to a boil. Add the potatoes and let it simmer over medium heat for about 15-20 minutes or unitl you can easily pierce the potatoes with fork. Drain the cooking liquid and mash the potatoes with a fork or a potato masher until it is smooth
• If you are using a pressure cooker like an Instant Pot, fill up the inner pot with 1 cup of water. Place the cut potatoes on a steaming basket. Close the lid and turn the pressure release valve to sealing. Press "pressure cooker" and make sure it's on high pressure. Set the timer to 10 minutes and then do quick release. Mash the potatoes with a fork or a potato masher until it is smooth
  
• The leftover mashed potatoes can be kept in the fridge, covered, for 2-3 days. I usually portion them out into 100-gram portion and wrap them tightly in cling wrap and freeze them. I use them whenever I want to in baking or cooking.

Prepare the batter:

• Combine oil and chocolate chips in a heat-proof bowl set over a pot of gently simmering water. Make sure the bowl doesn't touch the water. Let the chocolate melt over medium-low heat. This shouldn't take long, about a minute or so
  
• In another mixing bowl, add sugar, eggs, vanilla, cocoa powder, and salt. Whisk vigorously until the mixture is emulsified.
  
• Add the just warm mashed potatoes (make sure it's not hot so it won't "cook" the eggs) to the mixture and whisk again until combined
  
• Add the flour
  
• Use a rubber spatula to fold the flour mixture into the wet ingredients until you don't see any more streaks of flour
  
• Scrape the batter into the prepared pan. Smooth out the top. Sprinkle with chocolate chips all over the surface of the batter followed by a light sprinkle of flaky sea salt
  

Baking:

• Place the pan in the middle rack of the oven and bake for 20-23 minutes or until the edges are slightly puffy but the center still looks soft and slightly undone. DO NOT overbake. It took mine about 23 minutes.
  

Cool down:

• Let the brownies cool down in the pan set on a cooling rack completely. Once it has cooled down, I cover the pan with a wrap and put it in the fridge. I like it cold, but you can keep it at room temperature for 2-3 days
• I recommend allowing 12- 24 hours before cutting if you can wait that long! It gets better the next day!