01 - In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, and salt until homogeneously combined. Fold in chocolate chips if using. Store the mix in an airtight container in a cool, dry place for up to three months.
02 - Preheat the oven to 350°F. Grease and line an 8x8-inch baking pan with parchment paper to ensure easy removal.
03 - In a large bowl, blend the prepared brownie mix with melted butter, eggs, and vanilla extract. Stir gently until just combined to avoid overmixing.
04 - Spread the batter evenly in the prepared pan. Bake for 22 to 26 minutes or until a toothpick inserted near the center comes out with moist crumbs attached.
05 - Allow the brownies to cool completely in the pan before cutting into 16 equal squares.