We use quite a bit of carrots, celery, and onions (and other vegetables) around here, so one tip that a resource-savvy friend shared with me a few years ago, was to save the carrot peel, celery tops, and outer layer of onion in a ziplock freezer bag, then, when it became full, to use this when making a batch of vegetable stock. Brilliant! This has since become a routine practice in our home and I must say, it works beautifully. Once the stock is prepared, I simply freeze it in 2 and 4 cup containers and pull it out when needed.
2 TBSP olive or canola oil
Bag of carrot peel, celery, onion as described above -OR- if you do not have this handy, approximately 2-3 carrots, 2-3 stalks of celery, and 1 onion (all washed and chopped into ~1" pieces)
8 cloves garlic
8 sprigs fresh parsley
6 sprigs fresh thyme
2 bay leaves
slat and pepper to taste
2-3 quarts of water
1. Add oil to a 6-quart stockpot and heat over medium heat. Add vegetables (carrot, celery, onion, and garlic) and sweat for ~10 minutes, stirring occasionally.
2. Add water and increase heat to bring to a boil. Add in the remaining ingredients (fresh herbs, bay leaves, salt, and pepper). Lower heat and simmer uncovered for ~30 minutes.
3. Strain and discard vegetables. Cool and pour into containers (freeze or refrigerate as desired).