Mince garlic, set aside. Slice leeks, divide rings and soak in cold water to remove sand or dirt; drain. Peel and chop large russet potatoes. In a large stock pot, bring water to a boil and drop nettle in batches into water for 30 seconds, then transfer blanched nettle to ice water; drain.

In a large stockpot over medium heat, add butter, drained leeks and minced garlic. Saute until translucent, soft and fragrant.

Add stock and potatoes. Simmer until potatoes are tender.

Add nettle, nutmeg, lemon juice and zest, and return to a simmer.

Remove from heat. With an immersion blender (or use a blender in batches), puree soup until fairly smooth. Stir in heavy cream and salt and pepper to taste.

Ladle into serving bowls. Garnish with sour cream, creme fraiche or freshly grated aged cheese if desired.