Prep your pan: Heat oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or lightly grease.
Mix dry ingredients: In a large bowl, whisk flour, protein powder, baking powder, baking soda, and salt until well combined.
Flavor the sugar: In a separate bowl, use your fingers to rub lemon zest into the sugar until it smells fragrant and looks slightly damp. This releases the oils for better lemon flavor.
Combine wet ingredients: Add eggs, Greek yogurt, milk, oil, lemon juice, and vanilla to the lemon sugar.
Whisk until smooth with no yogurt lumps.
Bring it together: Pour wet ingredients into the dry. Stir gently with a spatula just until no dry streaks remain. Do not overmix.
Prep the blueberries: If using fresh berries, toss with 1 tablespoon flour to help prevent sinking.
If using frozen, do not thaw or toss—just add them frozen.
Fold in berries: Gently fold blueberries into the batter. A few streaks are okay; avoid overmixing.
Fill the tin: Divide batter evenly among cups, filling each about 3/4 full. Sprinkle tops with coarse sugar if using.
Bake: Bake 16–20 minutes, or until tops are set and lightly golden and a toothpick comes out with a few moist crumbs.
Cool: Let muffins rest in the pan for 5 minutes, then transfer to a wire rack to cool completely.
This helps set the structure and keeps the bottoms from steaming.