Yes, used to do this all the time for recipes for ds when he was a baby.
1 onion peeled
1 garlic clove peeled and roughly chopped
2 large carrots peeled
1 large leek washed
1 stick of celery
1 sprig of parsley
1 sprig of thyme
1 bay leaf
4 peppercorns.
Roughly chop all the veg chuck in your biggest pan and boil for at least one hour.#
Strain through a sieve, then squeeze the veg down with a masher to get remaining juice out of them.
I didn't always use all the herbs, think I only ever used the bay leaves and peppercorns as I had them anyway and it was fine.