
Prepare the vegetables by slicing the leeks, peeling and dicing the potatoes, and chopping the onion and garlic.
In a large pot, melt the butter over medium heat. Add the onions and garlic, cooking until they are soft and translucent, about 5 minutes.
Add the sliced leeks and thyme to the pot. Cook for an additional 5 minutes, stirring occasionally, until the leeks have softened.
Add the diced potatoes and vegetable stock to the pot. Bring to a boil, then reduce the heat to a simmer. Cover and cook for 15-20 minutes, or until the potatoes are tender.
Once the potatoes are tender, use an immersion blender to puree the soup until smooth. For a chunkier texture, blend only half the soup.
Stir in the double cream and season with salt and black pepper to taste. Heat through gently, but do not let the soup boil.
Serve hot, garnished with a sprinkle of fresh thyme or chopped parsley if desired.
