• Preheat the oven to 350 F (180 C) for conventional oven, 330 F (165 C) for convection oven
• Line 8 x 8 inch square pan with aluminum foil. Spray with some cooking spray to prevent sticking

Prepare the batter:

• Make sure you use very ripe bananas for the best result
  
• The mashed banana doesn't have to be smooth, some lumps are okay. Mash with a fork. Whisk oil, brown sugar, vanilla extract, and overripen mashed banana in a mixing bowl vigorously for about 30 seconds.
  
• Sift in salt, baking powder, baking soda, and flour into the bowl. Use a spatula to fold the dry ingredients into the wet.
  
• When it's almost combined but you still see some flour mix, add the toasted chopped walnuts and continue to fold until you no longer see dry pockets of flour. Don't overmix
  
• Scrape the batter into the prepared pan. Smooth the top with spatula to make sure the surface is even
  

Bake:

• Place the pan in the middle rack and bake for 25 minutes. The edges are slightly puffy but the wide center appears to be just about to set but still slightly undercooked. A toothpick test won't work here, so you have to count on your visual and judgement. DO NOT overbake. Remove from the oven

Cool down:

• Place the pan on the cooling rack and let it cool down completely in the pan. The edges pull away as it cools down
• Once it has cooled down completely, I like to cover it tightly with saran wrap and put this in the fridge. The cold makes the texture denser and fudgier, which I really like.

Serve:

• Even if you decide not to put this in the fridge, I still highly recommend serving this the next day if you can wait. You will be rewarded with a moist, fudgy, and even more pronounced banana flavor (if you use very overripe bananas)
• Cut into 9 pieces or 12 smaller pieces if you prefer and enjoy every bite of it!
• You can read more details on ingredients, substitutions, variations, and other tips in my post that may answer your questions not covered in the recipe card