- 3 tablespoons olive oil
- 1 large onion, peeled, half coarsely chopped, the other half kept whole
- 2 large celery stalks, sliced 1/2-inch thick
- 2 medium carrots, unpeeled and sliced 1/2-inch thick
- 2 garlic cloves, thinly sliced
- 1/4 teaspoon whole black peppercorns
- 8 sprigs flat-leaf parsley
- 8 sprigs basil
- 4 sprigs thyme
- 2 dried bay leaves
- Salt and pepper
- Heat the oil in a medium stockpot over medium until hot but not smoking. Add chopped onion and cook, stirring often, until beginning to brown, 10 to 15 minutes. Add celery, carrots, garlic, and peppercorns; cook, stirring occasionally, until vegetables are tender and lightly browned, about 10 minutes.
- Pour in enough water to cover vegetables by 1 inch (8 to 10 cups) and add herbs and remaining half onion. Season with salt and pepper and bring to a boil. Reduce heat to a gentle simmer and cook, uncovered, 1 hour.
- Pour stock through a fine sieve into a large bowl or another pot, pressing on vegetables to extract as much flavorful liquid as possible. Discard solids. If not using immediately, cool in an ice-water bath before transferring to airtight containers.
Vegetable stock can be refrigerated for up to 2 days or frozen for up to 3 months; thaw completely before using.