Preheat oven to 350 °F.
Line a 12 cup muffin tin with parchment paper liners, set aside.
Wash blueberries and dry with a paper towel, place in a medium sized bowl and sprinkle with 2 teaspoons of corn starch, gently stir to coat the blueberries with cornstarch, and set aside.
In a large mixing bowl, combine flour, 2/3 cup sugar, baking powder, and salt and mix with a wire whisk.
Wash and dry lemon, use a fine grater and zest the lemon peel directly into the flour mixture and mix.
Add milk, melted butter, and vanilla extract to the flour mixture.
Juice the lemon and add the juice to the flour mixture and stir until almost combined.
Add the blueberries and gently fold them in while scraping the bowl to incorporate any remaining flour.
Spoon 2 heaping tablespoons into each muffin liner and then evenly distribute remaining batter and blueberries (about 3 tablespoons per muffin).
Sprinkle 1/2 teaspoon of brown sugar over each muffin (optional).
Bake for 25 minutes (check for doneness by poking the center of the muffin with a skewer; should come out clean)