In a large bowl, combine the mashed potatoes, cheese, green onion, egg and ¼ cup all-purpose flour.
Add the remaining ½ cup of all-purpose flour in a shallow bowl.
Use a large cookie scoop to scoop out the potato mixture and drop in the bowl of flour. Coat the ball and then form a patty with your hands. Gently shake off any excess flour and place on a parchment-lined baking sheet. Repeat until done.
Pour about ¼ inch of oil into a large skillet and heat over medium heat. Add the potato patties without overloading the skillet. Cook for 3-5 minutes per side or until golden brown. Transfer to a paper-towel lined plate and repeat with the remaining patties.
Notes
If the mashed potatoes are well seasoned, you don't need any salt. However taste before mixing in the flour.
Use a large cookie scoop so you can get uniform size fritters.
Depending on the mashed potato consistency, you might need to add more flour so they don't fall apart.
To avoid using too much oil, use a nonstick pan so the fritters are easy to flip.
Once you add the fritter mixture to the oil, don't move them for 3-5 minutes before flipping so they create a crispy exterior.
Leftovers will last in the fridge for 3-4 days or in the freezer for 3 months.