Preheat the oven to 250°F degrees.

In a large bowl, whisk together the flour, sugar, baking soda, baking powder, and kosher salt until well combined and aerated. Pour the buttermilk on top, crack eggs into buttermilk, and add the 3 tablespoons of the melted butter to the mixture. Starting in the center and eventually moving towards the outside of the bowl, whisk everything together, just until all ingredients are incorporated and a thick, lumpy batter forms. (Do not overbeat.)

Heat a large nonstick griddle or skillet, preferably cast-iron, over low heat for about 5 minutes. Brush the cooking surface with some melted butter. Raise heat to medium–low, and using a measuring cup, ladle about 1/3 cup batter into the skillet. If you are using a large skillet or a griddle, repeat once or twice, being careful not to crowd the cooking surface.

Cook the pancakes until the bubbles that rise to the surface stop closing up immediately upon popping, 2 to 4 minutes. (If using blueberries, add 4 to 6 blueberries to each pancake before flipping and let them sink into the batter.0

When a small crater appears and remains such, and the bottom of the pancake looks golden-brown, then you can flip (a fish spatula makes the flipping much easier). Cook until the other sides are lightly browned, about 1 to 2 minutes. Keep in mind that the longer you cook the pancakes, the slightly faster this process will go as the pan or griddle will be more thoroughly heated through; trust your eyes and nose more than the time frame. Remove pancakes to a wire rack set inside a rimmed baking sheet, and keep in the warmed oven until all the batter is used up and you are ready to eat. In between batches of pancakes, brush your cooking surface with more melted butter.