Grate the zucchini with the large holes of a box grater or use a food processor. Measure 2 cups of shreds and set aside on a plate lined with paper towels so the zucchini shreds drain a bit while preparing the batter. See notes for removing excess wetness if necessary.
In a large bowl, combine flour, sugars, baking powder, baking soda, salt, and cinnamon.
Whisk eggs, Greek yogurt, and vanilla extract in a small bowl. Stir into the dry ingredients just until moistened. At this point, the mixture will be crumbly. (See picture #3 above.)
Stir grated zucchini into the batter just until combined. Don't overwork it; the batter will be thick. If necessary, add up to 1 Tablespoon of milk to achieve the desired consistency. (See picture #4 above.)
Liberally spritz paper insets with cooking spray. Spoon a heaping teaspoon of batter into the bottom of the muffin tin wells. This step will prevent blueberries from immediately sinking to the bottom.
Fold blueberries into the remaining batter, then fill the muffin wells ⅔ full. Don't overfill or the muffin tops might not set properly.
Bake for 20-25 minutes or until the muffins are firm and lightly browned on the top.
Allow the muffins to cool for 5 minutes in the pan, and then remove them to a wire rack to cool completely.
Video
Notes
See step-by-step pictures and more above.Top Tips:
Don't over-mix the batter, as this can develop the gluten too much and cause the muffins to collapse. Mix just until the ingredients are combined.
If the batter is too thick, add up to a tablespoon of milk. See the picture for step #5 to gauge the proper consistency.
Liberally spray muffin tin wells and paper inserts with non-stick cooking spray!
Let the muffins cool in the pan for about 5 minutes, then remove them to continue cooling. Cooling them in the pan for too long can make them soggy from the steam.
To prevent the blueberries from quickly sinking to the bottom of the muffin, layer a little batter in the bottom of the muffin cup before adding the batter with the blueberries.
Storage:
Countertop: Store the muffins you will use in the next 3-4 days in an airtight container on the countertop at room temperature. Line the container with a paper towel and arrange the muffins on top in a single layer for best results. Place another paper towel on top. The paper towel will absorb excess moisture as the muffins settle, so you won't end up with soggy muffins.
Freezer: Cool the muffins completely, and individually wrap each one in plastic wrap. Store them in an airtight plastic bag or container for about 2 months.