In a mixing bowl, combine leftover cooled mashed potatoes, all-purpose flour, salt, and melted butter. Stir until a cohesive dough forms, about 2-3 minutes.

Lightly flour a clean work surface, then turn the dough out onto it. Gently knead the dough for about 1-2 minutes until smooth and elastic.

Roll the dough into a circle approximately 1/4 inch thick. Cut the rolled dough into quarters, forming triangular shapes.

Place a non-stick skillet over medium heat. There's no need for oil, as the butter in the dough will provide sufficient greasing.

Carefully place each farl in the hot skillet and cook for about 3-4 minutes on each side until golden brown.

Once cooked, allow the farls to cool slightly on a wire rack. Serve warm with butter or your favorite toppings.