Preheat the oven to 375ºF. Grease or line a 12-cup muffin tin. Set aside.
In a large mixing bowl, beat the butter, lemon zest and sugar until well-combined.
Add the egg and vanilla and mix until well-combined, scraping down the sides as needed.
In a separate small bowl, toss the blueberries with ¼ cup of flour until the blueberries are coated.
Add the remaining 1 ¾ cups flour, baking powder, and salt to the batter.
Stir in just until mostly combined.
Add the buttermilk, and stir until the batter is combined. Don’t overmix.
Carefully fold in the blueberries. The batter will be thick.
Divide the batter among the prepared muffin tin cups.
Top the batter with the remaining 2 tablespoons of sugar.
Bake for about 12-18 minutes, or until a toothpick inserted in the center of a muffin comes out clean (it may have blueberry on it, and that’s ok).
Let muffins cool in the pan for 5 minutes before removing.
Notes
Butter: I use salted butter. If you're using unsalted butter, increase the total salt to 3/4 teaspoon.
Lemon zest: You'll need 1 medium lemon for the lemon zest.
Flour: It's important to properly measure the flour. If you have too much flour in the batter, you will end up with heavy or doughy muffins. To properly measure the flour, weigh it or sift/stir it to break it up. Lightly spoon it into a measuring cup and level.
Buttermilk: If you don't have buttermilk, you can use lemon juice from the lemon to make a homemade buttermilk substitute.