In a medium bowl, add the mashed potatoes, egg, dried parsley, and grated onion. Mix everything together until combined.
Check the mixture to see if it holds together. If the mixture is too wet, add a little flour and mix again.
Divide the mixture into 4 to 6 equal portions.
Shape each portion into a patty about ½ inch thick.
Place flour on a plate and press each patty into the flour to coat both sides.
Heat butter in a skillet over medium-low heat.
Place the patties in the skillet. Cook slowly until the bottom turns golden brown, then flip each patty with a spatula. Add more butter to the skillet if needed.
Cook until the second side turns golden brown and crispy.
Notes
Tips and Tricks
Chill the Potatoes - Cold mashed potatoes hold their shape better than warm ones. Make sure your leftovers are fully chilled before you start.Don't Skip the Flour Coating - The flour creates a crispy crust on the outside. Press each patty firmly into the flour so it sticks.Use Low to Medium Heat - Cooking the patties slowly helps them get crispy without burning. If the heat is too high, the outside will burn before the inside warms through.Add Cheese for Extra Flavor - Mix ¼ cup of shredded cheddar cheese into the potato mixture before forming the patties.Make Them Smaller for Appetizers - Form smaller patties to serve as finger food or appetizers at parties.Freeze for Later - Shape the patties and freeze them on a baking sheet. Once frozen, transfer them to a freezer bag. Cook directly from frozen, adding a few extra minutes to the cooking time.Reheat in the Oven - Place leftover potato cakes on a baking sheet and warm them in a 350°F oven for about 10 minutes to restore their crispiness.