Place your chicken cutlets between two sheets of plastic wrap and pound them with a mallet until they're an even thickness throughout. This step matters because uneven cutlets cook unevenly, leaving thin edges dry while the center stays underdone.
Add the flour to one shallow dish and season it with salt and pepper. In a second dish, whisk together the egg and milk until smooth. In the third dish, combine the panko with the chopped oregano, rosemary, and thyme.
Dredge each cutlet first in the seasoned flour, shaking off any excess. Dip it into the egg mixture, letting the extra drip away, then press it firmly into the herby panko so the coating sticks on all sides.
In a large skillet over medium heat, melt the butter together with the vegetable oil. Let the mixture heat until it's shimmering but not smoking, since this combination gives you rich flavor without burning too quickly.
Add the breaded cutlets to the skillet and cook for 3 to 4 minutes per side, until deeply golden and crisp. Avoid overcrowding the pan, and work in batches if needed so each cutlet gets even contact with the heat.
Transfer the cooked cutlets to a wire rack so the bottoms stay crisp instead of steaming. Sprinkle with a little flaky sea salt right away, then let them rest for a couple of minutes before slicing or serving.