Step 1: Heat the oven to 325 degrees. Whisk flour, sugar, baking powder, baking soda and kosher salt together in a bowl. Using the whisk, make a well in the center. Pour the buttermilk into the well and crack eggs and vanilla extract into buttermilk. Pour the melted butter into the mixture. Starting in the center, whisk everything together, moving towards the outside of the bowl, until all ingredients are incorporated. Add in blueberries. Do not overbeat (lumps are fine). The batter can be refrigerated for up to one hour.
Step 2: Heat a large nonstick griddle or skillet, preferably cast-iron, over low heat for about 5 minutes. Add 1 tablespoon of butter or oil to the skillet. Turn heat up to medium–low and using a measuring cup, ladle ⅓ cup batter into the skillet. If you are using a large skillet or a griddle, repeat once or twice, taking care not to crowd the cooking surface.
Step 3: Flip pancakes after bubbles rise to surface and bottoms brown, about 2 to 4 minutes. Cook until the other sides are lightly browned. Remove pancakes to a wire rack set inside a rimmed baking sheet, and keep in heated oven until all the batter is cooked and you are ready to serve.
