Make the maple butter
Put all the ingredients in a food processor and process, scraping down the sides of the bowl if necessary, until the mixture becomes smooth and uniform. Transfer to a large piece of plastic wrap, wrap it, roll it into a log and secure the ends as if it were a sausage. Refrigerate for at least an hour to a couple of days before serving.
Make the pancakes
In a large bowl, mix together the flour, cornmeal, sugar, baking powder, baking soda, and salt. In a medium bowl, whisk the buttermilk with the oil, eggs, and vanilla. Gently whisk the buttermilk mixture into the flour mixture until it’s mostly uniform (a few lumps are fine).
Heat a large stovetop griddle or large (12-inch) heavy-duty pan (like a cast-iron skillet) over medium heat until a droplet of water immediately evaporates upon hitting the pan. Melt a small pat of butter in the pan, pour in the batter (about 1/3 cup for each pancake), and then sprinkle with the blueberries. Leave space between each pancake so flipping them isn’t a problem. Cook the pancakes until bubbles form on top, the cakes set around the edges, and the bottoms brown, about 2 to 3 minutes. Flip and cook on the other side until they brown and the cakes become just firm to the touch, about 2 more minutes. Serve immediately topped with a pat of the maple butter.