In a small bowl, whisk together the flour, baking powder, salt, and sugar.
Place the egg whites into a large metal bowl and set aside.
In a medium bowl, add the egg yolks, yogurt, milk, olive oil, sourdough starter, and banana, if using. Whisk the wet mixture really well.
Slowly add the dry mixture into the wet mixture, stirring as you go, until all the dry bits are just incorporated. If it looks too wet, stir in a bit more flour. If it is not wet enough, stir in a bit more milk.
Heat up your cast iron or non-stick skillet on medium-high. You want it hot enough to give the pancakes good color on the surface while letting them cook through.
Beat your egg whites into stiff peaks. Fold in the resulting foam gently into the batter; it will get fluffy and light.
Use a quarter cup size scoop to drop the batter into the lightly oiled, hot skillet. Let the pancakes cook on one side until you see bubbles starting to form and pop on the surface. Flip and cook a bit more until nicely colored, 4 to 5 minutes in all.
I like to cook all the pancakes and save them on a big platter in a slightly warmed oven. Enjoy with some butter and maple syrup, or a homemade blueberry sauce.