While your frying pan and butter are heating up, mix the flour and the sodium bicarbonate together. Putting these ingredients in a closed plastic container and shaking vigorously works well.
Stir together the water, egg whites and vinegar.
When you see that the frying pan is hot and the butter is sizzling, drop the water, egg whites and vinegar at once in the dry mixture.
Blend quickly. Even if still lumpy, drop in your hot (medium high) frying pan.
Look at the baking soda reacting with the vinegar to produce those nice bubbles in the batter!
When the edges of the pancake are firm, it is ready to turn over. It's best
to turn the pancake over a little earlier than with normal pancake to capture the bubbles in.
Serve with fruit or syrup. The recipe for the caramelized apples shown in the photograph can be found here.