Combine 2 cups leftover mashed potatoes, a heaping 1/3 cup flour, 2 tablespoons milk and 1 tablespoon chopped mixed herbs in a bowl; knead until smooth. Season with salt and pepper. Divide into 4 balls on a floured surface and flatten each into a 3-inch patty. Melt 1 1/2 tablespoons butter in a large skillet over medium-high heat; add the patties and cook until golden brown, 4 to 5 minutes per side, adding more butter to the pan as needed. Season with salt.