Wash and roughly chop vegetables (no need to peel). Add to a large stockpot. Add enough water to cover vegetables, about 1 quart per pound of vegetable.
Set over high heat and bring to a boil. This can take as long as 20 minutes, depending on how much broth you are making and your stove efficiency.
Once boiling, reduce heat to low, cover, and simmer for 1 hour.
After 1 hour, turn off heat and let cool slightly. Strain stock into containers, or strain into a large bowl and portion from there.
Let cool to room temperature, then store in the refrigerator for up to 4 days or freezer for 6 months, until ready to use.
Notes
If freezing, make sure to leave 2 inches of headspace in containers to allow for expansion and prevent containers from cracking.