In a large bowl, sift flour, cocoa powder, cornstarch, baking powder and baking soda. Whisk to blend well. Add sour cream, milk, and corn oil. Mix well. Set aside.
In another bowl, beat egg with an electric mixer until light and fluffy. Add sugar in 4 batches, beating well after each addition. Continue beating until thick peaks form when beaters are lifted.
Fold in half of beaten egg to the batter to lighten it before adding the rest of the egg mixture. Lightly fold to avoid deflating it.
Brush waffle plates with some oil. Heat waffle maker to medium browning. Spoon ½ cup or less on the waffle plate, depending on the size of your waffle maker, and spread to the edges. Close the lid and cook the waffle, wait for the steam to dissipate before checking. Waffles should look dry and crisp up when paced on the plate. Continue cooking the rest of the batter.
To serve, top waffles with whipped cream, chocolate syrup, strawberries, and bananas.