from OnePerfectBite.blogspot.com

3 tablespoons vegetable oil or butter
1-1/2 cups diced onion
1 teaspoon minced garlic
1 large baking potato, cut in 1/2-inch dice to yield 2 cups
10 stalks of celery, trimmed and cut into 1/2-inch dice to yield 6 cups
1 small bulb fennel, trimmed, core and chopped (optional)
5 cups reduced-sodium vegetable or chicken broth
1 teaspoon apple cider vinegar vinegar
1 teaspoon celery salt (optional) or table salt to taste
1 large pinch pepper
2 tablespoons heavy cream (optional)
Celery leaves for garnish

1) Place oil or butter in a soup pot. Add onion and cook over medium heat until translucent, about 8 minutes. Add garlic and stir until fragrant, about 1 minute.
2) Add potatoes, celery and fennel (if using). Add broth and bring to a boil. Reduce heat and simmer until vegetables are tender, about 20 minutes.
3) Puree soup in batches using a blender or food processor. Pass puree through a strainer, pressing solids with the back of a spoon.
4) Return to a clean pot. Add pepper and celery or table salt. Stir in cream if using. Bring soup to a simmer and keep warm over low heat until ready to serve. Yield: 4 to 6 servings.