Preheat the oven to 350°F. Prepare a 9 x 9 baking pan by lightly spraying it with non-stick spray, line it with parchment paper leaving overhang on at least two sides, and lightly spray the parchment paper with the non-stick spray as well.
In a medium mixing bowl, whisk together the flour, cocoa powder, salt, and baking powder until evenly combined.
In a separate mixing bowl, use an electric hand or stand mixer to beat together the butter and sugar until light and fluffy.
Add in the eggs, milk, and vanilla to the mixing bowl with the butter and sugar and beat together at a low speed. The batter will be a little lumpy.
While beating on a low speed, gradually add in the dry ingredients, mixing just until combined. Scrape down the sides of the bowl with a rubber spatula. The batter will be thick.
Scoop out ⅓ cup of batter and set aside.
Fold the chocolate chips into the brownie batter.
Use a rubber spatula to spread the brownie batter into the prepared baking pan and even out the layer of brownie batter. Set aside for now.