Clean and cut the leeks- First, chop off the end of each leek and the tough, dark green tops. Chop the white and light green parts into 1/2-inch thick rounds and transfer to a bowl filled with cold water. Use your hands to separate the leeks, thus removing any dirt that may be stuck between the layers. Once clean, remove the leeks with a slotted spoon and set aside.
Prepare the bacon- Arrange bacon in a large skillet, working in batches if necessary. Turn heat to medium and cook the bacon until the edges start to curl (approximately 3-4 minutes). Flip the bacon and cook the other side until fully cooked and crispy. Remove the bacon to a clean plate lined with paper towels. Reserve the bacon fat.
Add two tablespoons bacon grease to a large soup pot set over medium-high heat. Add the onion to the pot. Sauté the onion for 3-4 minutes or until just started to soften and turn translucent.
Add the leeks, carrots and celery to the pot and mix well to combine. Cook an additional 3-4 minutes, stirring occasionally. Season with salt and pepper, and stir in the minced garlic and Italian seasoning. Cook for an additional minute.
Add the potatoes, cauliflower, and vegetable broth to the pot and stir to combine. Bring soup to a low boil, cover, and reduce heat to low. Simmer for 30 minutes, or until vegetables are soft and fully cooked.
Use an immersion (hand) blender, standing blender, or food processor to blend the soup. For a smooth soup, you may blend the whole thing, or, for a chunky soup, simply blend half the pot.
Return soup to the pot over low heat and stir in the Mariani Walnutmilk, adding more or less depending on how thick you prefer your soup. Season with additional salt and pepper, to taste.
Garnish with fresh chives, chopped bacon bits, and a drizzle of (good) olive oil, if desired. Enjoy!