Combine ingredients: add chicken carcass/bones to a large stock pot along with onion, carrots, celery, bay leaves, salt and pepper, and herbs (optional). Add enough cold water to cover everything by 1-2 inches -- about 10-12 cups of water.
Heat gently: Bring to a simmer slowly over medium high heat. Avoid boiling.
Skim the foam: as the stock begins to simmer, skim off any foam that rises to the top.
Simmer: low and slow over medium-low heat for at least 4-6 hours, but up to 12 hours for richer, deeper flavor.
Strain: Use a fine mesh trainer to remove all solids and discard.
Cool and store: allow the stock to cool completely, then place in airtight containers or jars and refrigerate. Fat will rise to the top and solidify - feel free to skim it off, but it is not required.