If your mashed potatoes are very soft or warm, chill them for 10 minutes so they're easier to shape. Leftover mashed potatoes work best because they're slightly drier.

In a mixing bowl, combine mashed potatoes, beaten egg, grated cheddar, chopped parsley, garlic powder, onion powder, salt, and pepper. Mix until everything is evenly incorporated.

Shape the mixture into patties: scoop about 1/3 cup per patty and flatten gently into rounds roughly 3 inches across. You should get about 8 patties.

Place the flour in one shallow dish, the beaten egg in another, and the breadcrumbs in a third. Lightly dust each patty in flour, dip into the beaten egg, then coat with breadcrumbs. Press breadcrumbs gently so they adhere.

Heat vegetable oil in a large skillet over medium heat. Once the oil shimmers, add patties in a single layer without overcrowding the pan.

Fry for 3-4 minutes per side, or until golden brown and crisp. Lower the heat slightly if the patties are browning too quickly before heating through.

Transfer to a paper towel-lined plate to drain briefly. Serve warm with sour cream, ketchup, or your favorite dipping sauce.

Optional finishing: sprinkle extra chopped parsley or a pinch of flaky sea salt before serving for a fresh, bright finish.