Preheat oven to 350 F. Grease an 8-in square baking pan, set aside.
In a medium-sized bowl, whisk together butter, avocado oil, and sugar. Whisk well for 1-2 minutes. Add the eggs and vanilla, whisk for an additional 2 minutes, until light in color.
In a small bowl, whisk together the flour, cocoa powder, and salt. Carefully fold the dry ingredients into the egg butter mixture, until just combined. Fold in the chocolate chips.
Pour the batter into the prepared pan, spread out evenly. Sprinkle the top with the chopped walnuts. Bake for 20-25 minutes, or until just set. (Brownies will be soft and chocolaty with a crackled top.) Allow the brownies to cool before slicing.
You can use an 8-in square baking pan, baking time may need to be adjusted.