Mix the baking powder with the flour.

In a bowl, beat the egg and sugar until the egg is dissolved. Add the milk and mix well. Gradually add the flour and mix until smooth. Add the oil and continue mixing until the oil is well incorporated.

Peel the ripe bananas and cut them in half lengthwise.

Place a flat-bottomed pan on the stove and add the butter. Use a spoon to spread the butter evenly, sprinkle with sugar, then arrange the bananas on top. Pour the batter over and tap the pan a few times to let the batter settle.

Cover with a lid and cook on very low heat. When the bottom is golden, use the lid to flip the cake and cook the other side until golden.