In a large mixing bowl, combine your leftover mashed potatoes with all-purpose flour, salt, and melted butter. Stir until a dough forms.

Lightly flour a clean surface, then transfer the dough to it. Knead gently for 1-2 minutes until smooth and elastic.

Roll the dough into a circle about 1/4 inch thick.

Cut the dough circle into quarters to create four equal pie-shaped farls.

Heat a non-stick skillet over medium heat. Cook each farl for about 3-4 minutes on one side until golden brown and crisp.

Flip the farls and cook for an additional 3-4 minutes until golden on the other side. Serve warm.