IN A MEDIUM MIXING BOWL, sift together the flour, sugar, salt, baking powder, and baking soda. Sprinkle the polenta over the other dry ingredients and toss until evenly mixed.

IN A SEPARATE BOWL, beat the eggs lightly with a fork, then add the buttermilk and the melted butter and whisk together briefly. Add the wet ingredients to the dry ingredients and mix until just blended-the batter will be a little lumpy. Gently fold in the blueberries until they are evenly distributed in the batter.

HEAT A LARGE CAST-IRON SKILLET or a griddle until it’s so hot that droplets of water dance across the surface, then brush it with vegetable oil. Using a ¼-cup measure or a 2-ounce ladle, pour the batter onto the pan or griddle and cook until large bubbles form on the top of the pancake and the edges begin to brown. Flip to the other side and cook for another minute or so, until the bottom is browned. Transfer to a paper towel-lined plate and keep warm in a low oven while you cook the remaining pancakes. Brush the pan or griddle with more vegetable oil as necessary as you cook the remaining batches.

SERVE THE PANCAKES WARM with a dollop of crème fraîche on top.