Wash the leeks to remove any soil, then trim off the end and the greener section, leaving the white & light green parts of the leek. Slice the remaining leek into thin rings.
Melt butter in a medium saucepan or Dutch oven on low heat, and add the garlic. When garlic begins to soften (after 1 minute), add the sliced leeks and mix well. Then cover and cook for 10 minutes.
Pour in the stock, add the potatoes, thyme, bay leaf, and bring to a boil.
Reduce heat and cook for a further 15 minutes till the potatoes are tender.
Discard the bay leaf, and blend the soup till it is smooth.
Stir in the cream (optional), taste and add salt if required and some black pepper, then garnish with fresh parsley or basil.
See post above for further details
To serve cold, chill for around 4 hours.
Select all purpose potatoes such as Yukon Gold or Désirée as they are not too waxy or starchy (floury).
Transfer to an airtight container and chill for up to 3 days.
This soup can be frozen without the cream. Transfer to a ziplock bag or airtight container and freeze for up to 3 months. Defrost in the fridge overnight, and reheat on the stovetop on medium heat till warm, then stir in the cream (if using).