1. Slice the white and light green parts of the leeks down the center or chop in circles. Rinse the grit from the layers and drain.
2. Melt butter over medium heat in a large stock pot. Add garlic and sauté for 30 seconds. Add the links and stir until soft and wilted, about 10 minutes. Watch so that the leeks do not brown.
3. Add potatoes, broth, bay leaves, thyme, salt and pepper to pot and bring to a boil. Cover and reduce heat to low. Simmer for 15 minutes, or until the potatoes are soft.
Remove thyme sprig and bay leaves. Use immersion blender to blend until smooth. Use caution if using a standard blender and work in batches.
Add heavy cream and bring to a simmer. You may add water if the soup is too thick.