Preheat oven to 350°F (175°C). Grease and flour an 8-inch springform 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 zest.
In a separate bowl, whisk together the flour, cornmeal, baking powder, baking soda, and salt.
Alternately add the dry ingredients and buttermilk to the wet ingredients, beginning and ending with the dry ingredients. Mix until just combined.
Pour the batter into the prepared springform pan and sprinkle with blueberries.
Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 10 minutes before removing it to a wire rack to cool completely.