Prepare the Leeks: Trim the white and light green parts of the leeks, discarding the dark green tops. Cut in half lengthwise and rinse thoroughly to remove dirt. Slice into ¼–½ inch pieces.
Sauté the Aromatics: Melt butter and olive oil in a large stockpot over medium heat. Add the leeks and sauté until soft, about 7–10 minutes, reducing heat if needed. Stir in the garlic and cook for 1 more minute.
Prepare the Potatoes: While the leeks cook, peel the potatoes, rinse them, and chop into 2-inch chunks.
Simmer the Soup: Add the potatoes, chicken broth, bay leaves, salt and pepper to the pot. Bring to a boil, then reduce the heat and simmer for 15 minutes, or until the potatoes are fork-tender.
Tip: you can exchange the salt for a tablespoon of chicken bullion for a deeper seasoned flavor.
Blend the Soup: Remove the bay leaves. Use an immersion blender to puree the soup directly in the pot, or ladle it into a countertop blender in batches, allowing the top to vent to release steam.
Garnish and Serve: Return the blended soup to the pot (if needed) and heat through. Serve in bowls with a sprinkle of croutons and a drizzle of olive oil for garnish. Consider garnishing with fresh herbs as well (see suggestions below).