Preparation Steps

• Position a rack in the center of the oven and preheat to 350°F. Line a 9x5-inch loaf pan with parchment paper leaving a 1-inch overhang on the long sides; lightly grease the parchment.
• In a large bowl whisk together the egg, brown sugar, granulated sugar, oil, sour cream (or yogurt), vanilla, and lemon zest until smooth and slightly glossy.
• In a separate medium bowl stir the 1 cup flour with the baking powder, baking soda, and salt until evenly combined.
• Add the dry mixture to the wet in two additions, folding with a spatula after each addition until just incorporated—stop as soon as there are no large streaks of flour to avoid overmixing.
• Gently fold the grated zucchini into the batter until distributed; a few streaks of zucchini are fine.
• Toss the blueberries with the reserved 1/4 cup flour in a small bowl (this helps them stay suspended), then fold the floured berries into the batter carefully so they don’t break. Reserve a tablespoon of berries to scatter on top if desired.
• Spoon the batter into the prepared pan, smooth the top with an offset spatula, and scatter the reserved blueberries. For a bit of crunch and shine, sprinkle a teaspoon of turbinado or coarse sugar over the surface.
• Bake for 50 to 60 minutes, checking at 50 minutes. The loaf is done when the top is golden, edges have pulled away slightly, and a toothpick inserted in the center comes out with a few moist crumbs but no raw batter.
• Let the bread cool in the pan on a wire rack for about 10 minutes, then lift it out using the parchment overhang and cool completely before slicing. Store wrapped at room temperature for up to 4 days or freeze slices for longer storage.