Position an oven rack in the center of the oven and preheat to 400 degrees F. Line a standard 12-cup muffin pan with paper liners.
In a large bowl, whisk the buttermilk, eggs and vanilla to blend. Combine 1 1/3 cups of the flour, the cornmeal, sugar, baking powder and salt in a processor, about 30 seconds. Drop in the cold butter cubes. Using on/off turns, blend until the butter is cut in finely and the mixture resembles a coarse meal, stopping occasionally to check the size of the butter pieces, (they should be the size of rice kernels). Pour the dry ingredients over the buttermilk mixture. Using a thin, flexible spatula and a few quick strokes, fold the batter together, turning the bowl as you fold.
In a medium bowl, combine the remaining 1 tablespoon flour and the frozen blueberries. Toss to coat the berries. Scatter the berries over the batter and fold in.
Using a rounded 1/3 cup of batter for each muffin, fill the paper liners, mounding the batter in the center. Use a knife tip or spoon to reposition at least 1 berry so it is showing on top.
Bake the muffins until puffed and browning at edges, and a tester inserted into the center comes out clean, 20 to 25 minutes. Let the muffins stand 5 to 10 minutes. Twist each muffin in place to loosen the edges from the pan. Lift the muffins out onto a rack and cool.