Mashed Potato Cakes
3 cups mashed potatoes, chilled or at room temperature
1/2 cup white cheddar cheese
2 medium scallions, thinly sliced (white and light green parts only, about 1/4 cup)
2 medium garlic cloves, minced
1 large egg, lightly beaten
1/3 cup all-purpose flour
2 tablespoons vegetable oil
Place all of the ingredients except the oil and salt in a medium bowl and stir to combine; set aside. Line a baking sheet with paper towels; set aside.
Heat the oil in a large frying pan over medium heat until shimmering, about 3 minutes. Drop 3 to 4 (1/3-cup) dollops of the potato-cheese mixture into the pan and spread each into a 3-inch patty.
Cook undisturbed until the bottoms are golden brown, about 4 to 5 minutes. Gently flip the cakes and cook until golden brown on the second side, about 4 to 5 minutes more.
Transfer to the prepared baking sheet and season with salt.
Repeat with the remaining potato mixture.