Preheat oven to 375-degrees. Lightly cover an 8-inch square baking pan with cooking spray.
In a large bowl, sift together the flour, baking powder and salt together.
In the bowl of an electric mixer, beat butter, sugar and zest on medium high until light, about 4 minutes. Add the eggs one at a time, scraping down sides of bowl as you go.
In another bowl, mix buttermilk and vanilla. Beat a third of flour mixture into butter mixture until nearly combined, then beat in half of buttermilk mixture. Repeat, ending with last third of flour mixture; beat until just combined. Stir in lemon juice.
Spread batter evenly in prepared pan and sprinkle blueberries on top, pressing down lightly. The blueberries will sink slightly as the cake cooks.
Bake until a toothpick inserted into center of cake comes out clean, 50 to 55 minutes. Let cool completely in pan on a wire rack.