In a large mixing bowl, combine the crumbled feta, grated kasseri (or graviera), and fresh parsley. Add the egg, breadcrumbs, olive oil, oregano, salt, and pepper. Mix until fully combined. The mixture should be thick but easy to shape into croquettes.
- Take small portions of the mixture (about 1 tablespoon each) and roll them into small cylindrical or ball shapes, about 1-1.5 inches long. Lightly dust your hands with flour to prevent sticking.
- Once all croquettes are shaped, roll them in breadcrumbs to coat evenly, ensuring a crispy exterior.
- Heat olive oil in a frying pan over medium heat. Add enough oil to cover the bottom of the pan.
- Fry the croquettes in batches, turning occasionally to ensure they cook evenly on all sides. Fry for 3-4 minutes, or until golden brown and crispy.
- Remove the croquettes from the pan and place them on a paper towel-lined plate to drain excess oil.
- Serve hot with tzatziki, a Greek salad, or on their own as a snack.