Undoubtedly your grandmother has an age-old recipe for chicken stock that she’s just waiting to teach you. But making your own veggie soup stock on the fly is pretty simple, and really only requires three ingredients: carrots, onions and celery (a magical combination the French call mirepoix).

Rather than throwing away carrot tops, onion skins and celery tips (all the stuff you don’t eat), save them in plastic containers in the freezer. Once you’ve got a few containers’ worth, toss them in a big pot and cover with water. Add an onion, sliced in half, plus two bay leaves and some pepper. Bring it to a boil, then lower the heat to medium and simmer, uncovered, for an hour. Then remove the mushy vegetable bits by pouring the pot over a strainer and voilà! You’ve got stock.

Freeze in yogurt tub-sized containers for making soups and stews, or in ice cube trays for small portions to add to sauces or sautés. Grandma will be so proud.

Here’s how you can put that stock to good use.