Leftover Potato Soup Good for using up leftover mash By Guest Contributor December 3, 2008 Soup Preparation Time Cook Time Servings0Ingredientsgood knob butter1 large onion, chopped1.25kg (2 3/4 lb) leftover mashed potatoes1L (1 3/4 pints) chicken stock100ml (4 fl oz) semi skimmed milksalt and freshly ground black pepper to tasteInstructions Step 1: In a medium soup pot, melt butter over low heat, and sauté onions until tender. Stir in the mashed potatoes, and then slowly add the chicken stock. Stirring, add milk (use more or less to achieve desired creaminess). Cook until heated through and season with salt and pepper to taste. Show Comments ▼