Preheat the oven to 350°F (175°C). Grease and flour a 9×9-inch baking pan.
In a large bowl, cream together the butter and sugar until light and fluffy.
Beat in the eggs one at a time, then stir in the lemon juice and lemon zest.
Combine the flour, baking powder, and salt; stir into the batter alternately with the buttermilk.
Gently fold in the blueberries.
Pour the batter into the prepared pan and spread evenly.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.