1 onion, cut in half
1-2 carrots, cut into thirds
2 stalks of celery
kitchen scraps (mine already included fennel, parsley, green onions etc)
If you like you can fry up your onion, carrots and celery first but I did not do this.
Add all ingredients into a large pot with around 6 cups of water.
Once liquid is cool enough store in freezer, I used zip lock bags in 2 cup lots.