Preparation Steps

• Position a rack in the center of the oven and preheat to 350°F. Line a 12-cup muffin tin with paper liners and give them a light spray with nonstick cooking spray.
• In a large bowl whisk together the whole wheat flour, cocoa powder, sugar, cinnamon, baking powder, baking soda, and salt until evenly combined and free of lumps.
• Grate the zucchini on the large holes of a box grater. Wrap the shredded zucchini in a clean kitchen towel and squeeze over the sink until no more liquid comes out; measure 1 cup and transfer to a medium mixing bowl.
• To the zucchini, add milk, eggs, melted butter, vanilla, and the orange zest. Whisk until smooth and uniform.
• Make a well in the center of the dry ingredients and pour in the wet mixture. Using a flexible spatula, fold the batter gently until barely combined — a few streaks of flour are okay. Overmixing will make the muffins tough.
• Fold the blueberries into the batter gently, reserving 8–10 berries to press on top of the muffins for a pretty finish.
• Spoon the batter into the prepared cups, filling each about three-quarters full. Top with the reserved blueberries and, if you like, a sprinkle of turbinado sugar for sparkle.
• Let the filled pan rest in the refrigerator for 8–10 minutes while the oven finishes heating; this brief chill helps the muffins rise evenly and results in a moister crumb.
• Bake for 18–22 minutes at 350°F, rotating the pan once halfway through baking, until the tops spring back lightly and a toothpick inserted in the center comes out with a few moist crumbs but not wet batter.
• Remove the pan to a wire rack and let the muffins cool in the tin for 5 minutes, then transfer the muffins to the rack to cool to warm or room temperature before serving.