Preheat a 20 cm soup pot for 1 minute and add the olive oil.
Toss in the potatoes and stir fry for 1 minute to coat the surface in olive oil.
Cover with the lid and heat for 1 1/2 minutes. The purpose of doing this is to produce a golden yellow color on the surface of the potatoes, which adds a rich flavor to the soup, otherwise the chowder will have a slightly powdery taste.
Add the onion slices to the potatoes and stir fry for 2 minutes.
Add the water and bring to the boil. Reduce to low and simmer for 20 minutes.
Add the garlic, cover the pot and cook for 2 minutes.
Add the celery, cover again and cook for 4 minutes.
Turn off the stove and using a stick blender, blend the soup to a smooth, creamy texture.
The texture of the soup is very important, so you should repeatedly taste it until there is no graininess. If you do not have a stick blender, you can use a food processor, but check the manufacturer’s instructions to see if your model can process hot food and if so, you will have to do it in batches.
Season the soup with salt and ground black pepper to your family’s liking.
Stir in the cream and taste test to see if you need more. Adjusting the amount of cream is very important for almost all Western-style soups, especially chowders: you need to add enough that it makes a difference and make it ‘creamy’. At this point, the soup is finished but it will need to cool before you cover it with the pastry.
Pour a thin layer of cream on the surface of the soup, and cool to room temperature with the lid on, but slightly ajar. If you completely seal the lid, condensation will drip down into the soup, and if you leave it off, the surface will form a skin.