Step 1: Preheat your oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease it thoroughly.
Step 2: In a large bowl, whisk together the 1 3/4 cups all-purpose flour, granulated sugar, baking powder, baking soda, and salt.
Step 3: In a separate medium bowl, whisk together the buttermilk, melted unsalted butter, large eggs, and vanilla extract until smooth.
Step 4: In a small bowl, toss the blueberries with the remaining 1 tablespoon of flour. This helps prevent them from sinking.
Step 5: Pour the wet ingredients into the dry ingredients. Mix with a rubber spatula or wooden spoon until *just* combined. A few lumps are fine; do not overmix.
Step 6: Gently fold in the floured blueberries and lemon zest until evenly distributed. Be careful not to crush the berries.
Step 7: Divide the batter evenly among the 12 muffin cups. Sprinkle with coarse sugar on top, if desired.
Step 8: Bake at 400°F (200°C) for 5 minutes, then reduce the oven temperature to 375°F (190°C) and continue baking for another 15-18 minutes, or until a wooden skewer inserted into the center comes out clean.
Step 9: Let the muffins cool in the muffin tin for 5-10 minutes before transferring them to a wire rack to cool completely. Serve warm or at room temperature.