Open Black Lager and let it come to room temperature.
In a 5-quart Dutch oven melt butter. Add bay leaves, leeks, carrots, celery root and garlic. Season with salt and white pepper. Saute vegetables 3-4 minutes. Add thyme, marjoram and 3-tablespoons chives.
Add Guinness Black Lager, chicken stock and potatoes. Bring to a full boil and reduce to simmer for 15 minutes.
Wisk in heavy cream, nutmeg, bring to a full boil. Stir to prevent cream from burning. Reduce to simmer for 30 minutes.
Remove bay leaves and puree soup using a hand blender. Season with salt and pepper to taste. Serve soup in warm bowls.