Start by preheating the oven to 350-degrees F.
Grease a Brownie Bar Pan with cooking spray. Alternatively, line an 8x8 baking pan with parchment paper - this will make it easy to remove the brownies from the pan.
Beat the butter and vanilla extract in the bowl of a stand mixer.
With the mixer on low, add the eggs one at a time.
In a medium mixing bowl, sift together the flour, baking powder, salt, and cocoa powder to remove any lumps.
Set the stand mixer to low again and add the dry ingredients to the bowl a little at a time.
Remove the bowl from the mixer and scrape down the sides.
Portion the batter into the brownie bar pan. I like to use a cookie scoop for this. If if you are using an 8x8 pan, you can use a spoonula to transfer the batter.
Bake for 18-20 minutes or until set.
Remove them from oven and set the pan on top of a cooling rack - allow them to cool for at least 30 minutes.