Melt the butter over medium-low heat in a large pot. Add leeks, cook while stirring until tender, 3-5 minutes. Add garlic and cook for 30 seconds. Add vegetable broth and potatoes. Cover and simmer over medium-low heat until potatoes are tender, ~30 minutes.Blend soup in batches in a blender until smooth. Return to pot and add salt and pepper to taste. Garnish with chopped fresh parsley. Makes 4-6 servings.