Preheat the oven and lightly coat a 9x13 baking dish with olive oil. In a shallow bowl, add flour with a pinch of salt and pepper. In another bowl, whisk the egg until smooth. In a third bowl, combine sourdough breadcrumbs, parmesan cheese, and a little salt or garlic salt. 

Place the large chicken breasts between pieces of plastic wrap and pound with a mallet until even in thickness. This step helps the chicken cook evenly and stay juicy.

Dredge each piece of chicken in the flour mixture, then dip it in the egg, and finally press it into the sourdough breadcrumb mixture, ensuring the ingredients fully coat both sides. Arrange the coated chicken in the prepared baking dish. Drizzle a little olive oil over the top and dot with small pieces of butter for extra flavor and browning.

Bake in the oven until the coating is golden brown and the chicken is cooked through. Remove the dish, spoon marinara sauce over each piece, and top with mozzarella and a little more parmesan cheese. Return to the oven for 10-15 minutes until the cheese is melted and bubbly. Serve.