In three small bowls about 25 cm in diameter (12 inches) place the flour, beaten egg and flour. Salt and pepper your beaten eggs.
Clean the chicken filets of any white membrane and remove the white connective thread. Do this by holding the connective thread by it's end on a cutting board with your thumb nail, pressing very firmly and with the edge of a samll knife sliding the meat off of it by scraped downward against the board to free the thread from the meat.
When all the filets are clean and ready, dry them with a paper towel.
Place a large piece of paper towel on the counter or a platter large enough to hold all the filets in one layer.
Take each filet and dip it in the flour and holding it over the bowl shake off any excess flour. Then dip it in the egg holding it up to let any excess egg run off, then dip the filet in the bread crumbs pressing it into the crumbs to get as much of them to stick to the filet as possible. (See above photo) Repeat the process and place each filet on the prepared platter or on the counter for cooking.
You can prepare the recipe up to this point and leave it for cooking later in the day or even the next day keeping it in the refrigerator well wrapped. If you do, take the filets out of the fridge at least one hour before you are going to cook them, unwrap them and replace the paper towel with a new dry piece and place all the filets out on it to dry out a bit before frying, turn them over once so they are as dry as possible before cooking.
Now in a pan large enough to hold all the filets comfortably, heat the oil and butter until hot. To tell if the pan is hot enough sprinkle in a few bread crumbs and if they begin to sizzle the oil should be hot enough.