Prep the pan and oven: Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving some overhang for easy removal. Lightly grease the parchment.

Grate the zucchini: Use the fine or medium holes of a box grater. Measure 1 1/2 cups loosely packed. Do not squeeze out the liquid.

Mix the wet ingredients: In a large bowl, whisk together the granulated sugar, brown sugar, oil, and vanilla until glossy and slightly thick, about 30 seconds.

Whisk the dry ingredients: In a separate bowl, combine the flour, cocoa powder, baking soda, and salt. Break up any cocoa lumps with a whisk.

Bring it together: Add the dry ingredients to the wet and stir until mostly combined. The mixture will look very thick and sandy—this is normal.

Fold in the zucchini: Add the grated zucchini and stir gently. Within a minute, the batter will loosen and turn glossy as the zucchini releases moisture. If using, fold in the chocolate chips.

Fill the pan: Spread the batter into the prepared pan, smoothing the top with a spatula. Sprinkle a few extra chips and a pinch of flaky salt if you like.

Bake: Bake for 25–32 minutes, until the center is set and a toothpick inserted in the middle comes out with moist crumbs but not wet batter.

Cool and slice: Let the brownies cool in the pan for at least 30 minutes. Lift them out using the parchment and cool another 10–15 minutes before cutting into squares.

Serve: Enjoy slightly warm for maximum fudginess, or at room temperature for clean slices and a chewier edge.