In a large bowl, whisk together the flour, cornmeal, sugar, baking powder, and salt. In another bowl, whisk together the egg yolks, melted butter, milk, and yogurt until smooth, and then add this to the flour mixture, whisking to combine the two. Let the batter rest for five minutes or so until it thickens (whole wheat flour absorbs more liquid than white flour).
In a clean bowl, or with a stand mixer, whisk the egg whites until they hold stiff peaks. Fold the egg whites gently into the batter.
Cut the fruit into relatively thin slices and set aside. (Not too thin, though: you want to taste the fruit, not have it disappear into the pancake.)
Grease a griddle or cast-iron pan with butter (or vegetable oil, if you prefer). Cook the pancakes over moderate heat, dropping several tablespoon sized scoops of the batter onto the hot griddle. Then decorate the top of the pancakes with the sliced fruit. I cover my pancakes with immodest amounts of fruit -- I like to have fruit in every bite -- but feel free to use less, of course. When bubbles appear on the top of the pancake -- peeking through where there is no fruit -- flip and then cook until the fruit is caramelized. Serve immediately, fruit up or down (depending on how photogenic or mangled your fruit looks).