makes 500ml/18fl oz
Put the oil in a large casserole dish over a medium heat. Sauté the leeks, carrots, celery, potato and garlic until slightly browned. Add 1.2 litres/2pt water and the remaining ingredients.
Bring to the boil, then reduce the heat and simmer, uncovered, for 1 hour. Strain the stock through a fine-mesh sieve and leave to cool.
Store in the refrigerator and use within 3 or 4 days, or divide into portions and freeze until needed.