Leave out butter until the butter becomes room temperature.
Preheat oven to 175°C ( 350°F).
Grease an 9" x 9" (23cm x 23cm) square pan.
Whisk eggs until light in a medium sized bowl.
Then add sugar, melted butter, and cocoa. Mix well.
Add flour, salt, baking powder, vanilla, and nuts.
Mix well with rubber spatula.
Pour into greased pan.
Bake for around 20 minutes in pre heated oven.
To tell when brownies are done, use a toothpick, stick it into the center, and pull it out.
The brownies need more time if there is wet batter on the toothpick.
If there are a few moist crumbs on the toothpick, the brownies are done.
Remove from the oven and let it cool down to room temperature.
Remove the brownies from the pan and let them chill in the fridge for a couple of hours.
(chilled brownies are easier to cut).See Notes.
Cut the brownies into 20 pieces.
Use a warm knife to cut, making sure to clean the blade after each cut for clean, neat edges.