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. Whisk in eggs, stirring until fully incorporated.
Add dry ingredients (baking soda, salt, flour and cocoa powder) to wet ingredients. Stir until combined. Fold in chocolate chips. Batter will be thick.
Spread batter into prepared pan. Bake at 350°F for 25-30 minutes. Let cool for 30 minutes before cutting.
Notes
A metal baking pan is recommended for best results. For glass or ceramic pans: Reduce heat to 325F. Cooking time will increase 2-3 minutes. A double batch in a 9X13 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.