Preheat oven to 350°F. Line a 9”X9” square metal baking pan with parchment paper or aluminum foil.
Melt butter and set aside till cool.
Whisk together butter, granulated sugar and vanilla extract in a large mixing bowl. Gently mix in eggs, stirring until fully incorporated. Avoid over-whisking eggs.
Add dry ingredients (baking soda, salt, flour and cocoa powder) to wet ingredients. Stir until combined. Fold in the chocolate chips. Batter will be thick.
Spread the brownie batter into the prepared pan. Bake at 350°F for 25-30 minutes. The brownies are done when the edges are set and the top is slightly puffy. A toothpick inserted into the center should come out with moist crumbs attached, not clean. Let cool in the pan for 30 minutes to set before cutting.
Notes
Cocoa Powder: Natural unsweetened cocoa powder such as Hershey's or Nestle is recommended.To use Dutch-process cocoa powder: Omit the baking soda and add ½ teaspoon baking powder. A metal baking pan is recommended for best results. For glass or ceramic pans:Reduce heat to 325°F. Cooking time will increase 2-3 minutes. A double batch in a 9X13-inch glass pan takes approximately 45 minutes. Chocolate Chips: I recommend using Hershey's Dark Chocolate Chips. A semi-sweet chocolate chip will also work. The chocolate chips you use should still be slightly sweet. Lining the pan: I like to the line the pan with foil or parchment paper to easily remove brownies from pan for cutting. For chewier edges use foil, for softer edges and even baking, parchment paper is recommended. If you prefer to grease the pan instead, that is an option too. High Altitude Bakers: Add 1-2 tablespoons of water or brewed coffee to the batter.For extra fudgy brownies, omit the baking soda and add 1-2 teaspoons of a neutral flavored oil (like canola oil) to the batter.