Preheat your oven to 350°F (177°C).

Lightly grease a 9×13-inch baking pan, or line it with parchment paper leaving a 1–2 inch overhang on two sides for easy lifting.

Set a cooling rack nearby so the bars can cool once they come out of the oven.

Pro tip: Lining the pan with parchment makes it much easier to remove the whole slab and slice neatly.

Trim the ends off 2 medium zucchinis and grate them on the large holes of a box grater or using the grater disk on a food processor.

If the zucchini looks very wet (summer zucchini can be watery), place the grated zucchini in a clean kitchen towel and squeeze gently to remove excess liquid — you want to remove excess water, not all moisture.

Pro tip: Don’t over-squeeze — you want the zucchini to keep some moisture because it’s what keeps the bars tender.

In a medium bowl, whisk together 2 cups all-purpose flour, 1 tsp baking powder, ½ tsp baking soda, ½ tsp salt, 2 tsp ground cinnamon, and ¼ tsp ground nutmeg until evenly combined.

Give the mixture one last sift or whisk to remove any lumps and ensure even distribution of the leaveners.

Pro tip: Whisk continuously when combining to prevent pockets of baking powder or clumps of spice—this helps the bars bake evenly.

In a large bowl, whisk 1 cup granulated sugar and ½ cup packed brown sugar with ½ cup vegetable oil until the sugars are damp and the mixture looks cohesive.

Beat in the 2 large eggs one at a time until fully incorporated.

Stir in 2 tsp vanilla extract.

Pro tip: If using a hand or stand mixer, mix on medium speed just until the eggs are incorporated—overmixing can whip too much air into the batter.

Add the dry ingredients to the wet ingredients in two additions, folding gently with a rubber spatula after each addition until mostly combined.

Fold in the 2 cups grated zucchini until evenly distributed — scrape the bottom and sides of the bowl so there are no streaks of flour.

The batter should be thick but pourable; avoid vigorous stirring once the flour is in to keep the texture tender.

Pro tip: Fold, don’t beat. Overworking the batter develops gluten and makes the bars dense rather than tender.

Pour the batter into your prepared 9×13 pan and use a spatula to spread it into an even layer.

Tap the pan gently on the counter to settle the batter and remove large air pockets.

Place the pan in the preheated oven on the center rack. Bake for 25–30 minutes.

To check for doneness, insert a toothpick into the center — it should come out with a few moist crumbs but not wet batter. If the toothpick has batter, bake for an additional 3–5 minutes and check again.

Pro tip: Ovens vary — start checking at 25 minutes so you don’t overbake. A slightly moist crumb is better than a dry bar.

Remove the pan from the oven and let it cool on a rack for at least 20–30 minutes.

If you’re frosting, let the bars cool completely (cooling prevents the frosting from sliding off). Beat the frosting ingredients (8 oz cream cheese, ½ cup butter, 3 cups powdered sugar, 1 tsp vanilla) until smooth, then spread over cooled bars.

If not frosting, allow the bars to cool slightly, then lift from the pan using the parchment overhang and transfer to a cutting board.

Pro tip: For the cleanest slices, chill the frosted slab for 15–20 minutes before cutting, and use a sharp knife wiped clean between cuts.

Use a sharp knife to slice into bars — aim for 2×2-inch pieces for snack-sized bars (adjust to your preference).

Store any leftovers in an airtight container in the fridge for up to 4–5 days (frosted) or at room temperature for 2 days (unfrosted).