Prep the pan: Heat the oven to the temperature listed on your Duncan Hines box, usually 325–350°F (163–177°C). Line an 8x8 or 9x9 metal baking pan with parchment, leaving overhang for easy lifting. Lightly spray.

Whisk the wet ingredients: In a large bowl, whisk eggs, oil, melted butter, water or milk, vanilla, and salt until smooth and slightly frothy, about 30 seconds.

Add the mix: Sprinkle the Duncan Hines brownie mix over the wet ingredients. Stir gently with a spatula until just combined. Do not overmix—stop when you no longer see dry streaks.

Fold in extras: Stir in chocolate chips or chunks. You can also add 1/2 cup chopped walnuts or pecans here if you like.

Create a shiny top (optional): Sprinkle 1 tablespoon of granulated sugar evenly over the batter and lightly fold once or twice. This helps form that crackly crust.

Spread and smooth: Pour the batter into the prepared pan. Use the spatula to spread it into the corners and level the top.

Bake: Bake according to the box guidelines, usually 23–28 minutes for an 8x8 pan, or a bit less for a 9x9. Start checking at the earliest time. They’re done when a toothpick comes out with a few moist crumbs, not wet batter.

Cool for clean slices: Let the brownies cool in the pan on a rack for at least 30–45 minutes. Lift out using parchment and cut with a sharp knife. Wipe the knife between cuts for neat squares.