Instructions:
- Melt half the butter in a large heavy-bottomed Dutch oven or stockpot over medium-low heat. Add the sliced leeks and minced shallots. Sweat gently, stirring occasionally, until very soft and translucent (about 8-10 minutes). Do not allow them to brown.
- Add the minced garlic and cook for 1 minute until fragrant. Add the remaining butter, let it melt, then sprinkle in the flour. Whisk constantly for 2 minutes to cook out the raw flour taste, creating a light roux.
- Gradually whisk in the stock, ensuring no lumps form. Add the diced potatoes, dried thyme, and bay leaf. Bring the mixture to a gentle simmer.
- Reduce heat to maintain a steady, gentle simmer. Cook, partially covered, for 18–20 minutes, or until the potatoes are completely fork-tender.
- Remove and discard the bay leaf. Use an immersion blender directly in the pot to blend the soup until perfectly smooth and velvety. Alternatively, carefully blend in batches using a standard countertop blender, ensuring the lid is vented.
- Stir in the heavy cream. Heat through gently for 2–3 minutes, ensuring the soup does not boil after the cream is added. Taste and adjust seasoning generously with salt and freshly ground black pepper.
- Ladle the soup into bowls and garnish generously with chopped fresh chives and a final grind of black pepper before serving.