In a large mixing bowl, combine leftover mashed potatoes, all-purpose flour, baking powder, salt, and black pepper. Mix until a soft, cohesive dough forms, about 2-3 minutes.

If desired, gently fold in chopped green onions and shredded cheese at this stage. Mix until evenly distributed.

Transfer the dough onto a floured surface, and divide it into eight equal portions. Shape each portion into a patty about ½ inch thick.

Lightly dust each patty with flour to prevent sticking. Set aside while you heat the frying pan.

In a large skillet, melt butter over medium heat until it begins to bubble.

Gently place the potato patties into the skillet, cooking for 4-5 minutes on each side until golden brown.

Once fried, remove the cakes and place them on a paper towel-lined plate to drain excess grease.

Serve warm as a snack, side dish, or breakfast treat topped with your favorite ingredients.