Prepare the chicken: Place the chicken breasts between two sheets of plastic wrap or place them in a large freezer bag in batches. Use a meat pounder to pound the chicken breasts to an even thickness of about 1/4 inch each.
Season the chicken: Season the chicken breasts with salt and pepper on both sides.
Set up the breading station: Arrange three breading pans or shallow dishes in a row to set up a breading station. In a mixing bowl, whisk together the bread crumbs, grated Parmesan cheese (optional), paprika, garlic powder, onion powder, ground mustard, and ground thyme.
Pour the all purpose flour in the first pan or dish. This will be the first step for breading the chicken schnitzel. Next, place the eggs in the second dish. Finally, add the bread crumb mixture to the third breading pan or shallow dish.
Bread the chicken: Dredge each chicken breast in the flour, then shake off the excess flour. Next, dip the floured chicken breast into the beaten eggs, and then let the excess drip off.
Next, coat the chicken with the seasoned breadcrumb mixture in the third breading pan or dish, pressing gently to ensure each chicken breast receives an even coating.
Fry the chicken schnitzel: Heat cooking oil or clarified butter in a large skillet over medium high heat. Add the breaded chicken breasts to the skillet and cook for 3 to 4 minutes per side or until the chicken is golden brown and crispy, and fully cooked, having reached an internal temperature of 165°F.
Place the cooked chicken schnitzels on a paper towel lined plate to drain any excess oil from cooking.
Prepare the lemon sauce: First, make a roux. Melt the butter in a small saucepan over medium heat. Once the butter is melted, add the flour and whisk continuously for about 1 to 2 minutes until the flour and butter mixture is golden brown.
Whisk: Slowly whisk in the chicken broth, continuing to stir until the mixture is smooth and begins to thicken.
Once the sauce has thickened, whisk in the heavy cream, and cook the lemon sauce for another 2 to 3 minutes until it thickens slightly.
Stir in lemon: Stir in the lemon juice and lemon zest, then season the sauce with salt and pepper to taste. Cook over low heat for another minute to allow the flavors to meld, whisking constantly.
Remove from heat: Remove the creamy lemon sauce from heat. If the sauce is too thick, you can thin it out with a little more chicken broth or cream. Garnish the lemon sauce with chopped fresh parsley.
Serve: Plate the chicken schnitzel, and drizzle the creamy lemon sauce over the top. Garnish with lemon wedges and chopped fresh parsley. Serve the chicken schnitzel immediately with your choice of sides.