1 cup all-purpose flour
3 tablespoons plus 1 teaspoon granulated sugar
1 1/2 teaspoons baking powder
1/2 teaspoon coarse salt
3/4 cup whole milk
1 large egg, room temperature
2 tablespoons unsalted butter, melted, plus 1 tablespoon for pan
1 cup blueberries
Place an oven rack in the upper third position. Preheat the oven to 375°F. Place a 10-inch cast iron skillet in the upper rack. Whisk the flour, 3 tablespoons granulated sugar, baking powder, and salt in a bowl. Whisk the milk, egg, and melted butter in a separate bowl. Whisk the milk mixture into the flour mixture until just combined (a few lumps are okay).
Remove the skillet from the oven and swirl the remaining 1 tablespoon of butter in the skillet to coat. Pour the batter into the skillet and smooth the top with an offset spatula. Sprinkle evenly with blueberries and remaining 1 teaspoon granulated sugar.
Bake until golden brown and cooked through, about 25 minutes. Remove from the oven. Allow the pancake to cool 5 minutes. Slice and drizzle with blueberry syrup.