Prepare the Baking Pan: Preheat your oven to 325°F (165°C). Lightly coat an 8x8-inch square baking dish with nonstick cooking spray. Line the dish with parchment paper so it overhangs on the sides, then lightly spray the parchment as well. This setup will prevent sticking and help lift the brownies out easily after baking.
Mix the Dry Ingredients: In a medium mixing bowl, whisk together the granulated sugar, all-purpose flour, cocoa powder, powdered sugar, dark chocolate chips, and salt. Stir until well combined, ensuring no lumps remain in the mixture. The chocolate chips will melt slightly during baking, adding pockets of richness to the brownies.
Blend the Wet Ingredients: In a separate large bowl, whisk the eggs, oil, water, and vanilla extract until fully blended. The mixture should be smooth and slightly glossy.
Combine Wet and Dry Mixtures: Gradually add the dry ingredients to the bowl with the wet mixture. Use a spatula or wooden spoon to stir gently until the batter just comes together. It will be thick and dense, which is key for that fudgy texture. Avoid overmixing to prevent a cakey result.
Spread and Bake: Pour the thick brownie batter into your prepared pan and use a spatula to spread it evenly across the surface. Place the pan in the preheated oven and bake for 40 to 48 minutes. The brownies are done when a toothpick inserted near the center comes out with only a few moist crumbs attached (not wet batter).
Cool and Slice: Remove the pan from the oven and place it on a wire rack. Let the brownies cool completely in the pan—this will take about 2 hours. Once cooled, lift them out using the parchment paper and slice into 16 squares.