Preheat an oven to 375 degrees. Generously butter twelve 1/2-cup muffin-tin cups.
In a large bowl, using an electric mixer set on high speed, beat the butter until light and fluffy. Gradually add the granulated sugar, continuing to beat until light, about 2 minutes. Add the eggs, one at a time, beating well after each addition. Beat in the vanilla, baking powder and salt.
Using a rubber spatula, fold in half of the flour, then half of the milk. Repeat with the remaining flour, all of the cornmeal and the remaining milk, then fold in the blueberries.
Spoon the batter into the prepared muffin cups, filling each cup two-thirds full and evenly distributing the blueberries. Sprinkle the brown sugar evenly over the tops.
Bake until golden or a toothpick inserted into the center of a muffin comes out clean, 35-40 minutes. Transfer the pan to a rack and let cool for 15 minutes. Turn out the muffins onto the rack and serve warm or at room temperature.
Wrap any cooled leftover muffins airtight and store at room temperature for up to 2 days.
Recipe reprinted by permission of Weldon Owen. All rights reserved.