Preheat oven to 350 degrees. Lightly oil a standard loaf pan and cut a piece of parchment to fit inside, with the long edges overhanging by 2 or 3 inches.
Whisk the cornmeal, flour, baking powder and salt together in a small bowl.
Beat the eggs, egg whites and sugar in a heavy-duty mixer fitted with the paddle attachment until pale and creamy. On low speed, slowly pour in the oil. Mix in the sour cream.
Stir in the dry ingredients until just blended, then fold in 1 cup of the blueberries.
Scrape the batter into the prepared pan and sprinkle the remaining blueberries over the top. Bake for 1 hour plus 25-30 minutes. The top of the cake should be golden and a toothpick inserted in the top of the cake should come out clean.
Cool the cake on a rack. Once it's completely cool, use the parchment paper to lift the cake out of the pan.
Tips and variations:
Add a tablespoon or so of fresh lemon zest to the batter.