Beat the egg and milk in a small bowl.
In a large bowl, combine the flour, sugar, and salt. Add the milk mixture, stirring to make a thin batter, being careful not to overmix. Fold in the melted butter.
Grease each round cup in the pan with oil. Pour about 2 tablespoons of batter into each of the greased cups and cook until bubbles form on the top, about 1 minute. Turn with a spatula and cook on the second side until golden, about 1 minute. Remove from the pan and repeat with the remaining batter.
Serve hot with sour cream, or lingonberry jam.