Soggy muffins are a sad sight—and taste! Use the power of salt to keep your zucchini muffins light and fluffy (but not salty).
Adjust oven rack to middle position and heat oven to 325 degrees. Spray 12-cup muffin tin, including top, with vegetable oil spray.
Use chef’s knife to trim off ends of zucchini. Shred zucchini on large holes of box grater.
Set fine-mesh strainer over large bowl. Transfer shredded zucchini to strainer and sprinkle with ½ teaspoon salt. Use rubber spatula to stir until combined. Let sit for 20 minutes to drain.
Place clean dish towel on counter. When salted zucchini is ready, transfer to center of dish towel. Gather ends of towel together, twist tightly, and squeeze hard over sink, draining as much liquid as possible. Discard any liquid from large bowl.
In medium bowl, whisk together whole-wheat flour, all‑purpose flour, cinnamon, baking powder, baking soda, nutmeg, and remaining 1 teaspoon salt.
In now-empty large bowl, whisk together eggs, oil, vanilla, and 1 cup sugar. Add zucchini and use rubber spatula to stir until combined.
Add flour mixture and use rubber spatula to gently stir until just combined and no dry flour is visible. Do not overmix.
Spray ⅓-cup dry measuring cup with vegetable oil spray. Use greased measuring cup to divide batter evenly among muffin cups. Sprinkle remaining 2 tablespoons sugar evenly over batter in each muffin cup.
Place muffin tin in oven. Bake until muffins are golden brown and toothpick inserted into center of 1 muffin comes out clean, 25 to 30 minutes.