You can use the ingredients of items that are leftovers and not usually eaten. You can use a bunch of parsley stems, the insides of the onions, ends of mushrooms, a leftover piece of escarole, ends of potato, ends of carrots, pieces of celery and some parsnip. You can store these leftovers in a plastic bag and refrigerate it. However you have to use this in for days. Use a large pot and fill it with one third of this stuff. You can add all kinds of leftover pieces except Cruciferous vegetables like no cabbage, cauliflower, broccoli, collard, turnips etc. Because these have a number of sulfur compounds and they make the taste of the stock very stinky. Now add a bay leaf and some garlic to the stock. In case you want you can put in whole cloves of garlic. Add some pepper corn in it. Now add lots of water. Now put the pressure cooker lid on and then heat till the pressure starts in the cooker. When the little yellow part on the pressure cookers comes up then it shall indicate the pressure has risen in the cooker. If you add lots of water then it shall take a lot of time to build the pressure. Once the pressure comes on you have to allow it to cook for five minutes and then switch of the heat. Then allow it to remain till the pressure comes down. Now you have to strain the stock to remove all the solid ingredients. If you prepare a large pot of stock then you can save the money that you spend on purchasing from the market which has lots of sodium in it. After cooling you can store it and then refrigerate. That‚Äôs it.