Add corn cobs, peppercorns, onion, parsley, and 8 cups water to medium saucepan. Bring to boil over high heat; reduce heat and let simmer 1 hour. Strain and discard solids (see recipe note) using a fine mesh sieve optionally lined with cheesecloth for clear stock. Use immediately or let cool completely and refrigerate up to 1 week, or freeze for up to 2 months.
Notes
To make straining the liquid easier, lift out and discard the boiled cobs with a large slotted spoon before pouring the liquid through a fine strainer lined with cheesecloth (optional).