Preheat oven to 350F. Grease a 9" square pan, (I like to use Bakers Joy spray)
Zest your lemon, then juice it and set aside
In a small bowl or cup, mix the milk with 1 Tbsp of fresh lemon juice and let it sit for five minutes.
In a separate small mixing bowl, whisk together the flour, baking powder, and salt. Set aside
In your mixer bowl, beat together the butter, sugar and lemon zest for 2-3 minutes or until nice and creamy
Scrape down the mixer bowl, add the egg and vanilla, and continue to beat until well combined
Add the flour mixture and the milk mixture and mix on low speed until just combined
Toss the blueberries with 1 Tbsp of flour and gently stir them into the batter with a spatula
Dump the batter in to your prepared pan and use your spatula to gently spread it to the edges
Sprinkle the 1 Tbsp sugar all over the top of the batter
Bake at 350 for 40-45 minutes or until a toothpick comes out with no wet batter on it, just moist crumbs
Remove from the oven and place the pan on a cooling rack for at least 30 minutes before serving