In a bowl, combine the flour, salt and sugar. Gradually pour in the milk, stirring constantly, until a smooth batter is formed. Add the eggs, one at time, stirring well each addition. Stir in sliced bananas.
Heat oil and butter in a nine inch non-stick skillet over medium heat. Pour the mixture in by spoonfuls, spreading the mixture evenly across the pan. When the bottom has turned a golden brown, turn the frittata and cook over low heat until golden brown on the other side. Sprinkle with sugar and serve warm.