Potato Celery Root Soup

3 tablespoons olive oil
1 fresh onion, chopped
2-3 cloves garlic, minced
5 potatoes, cut into 1 inch cubes
1 celery root, peeled and cut into 1 inch cubes
6 cups vegetable or chicken broth
1 cup milk or cream (optional)
salt and pepper, to taste
1 bunch chard, stems removed
Dash of cider vinegar
Heat 2 tablespoons of the olive oil in a Dutch oven or your soup pot over low heat. Add the chopped onions and minced garlic. Sauté slowly, stirring occasionally, for about 10 minutes, or until the vegetables have begun to caramelize, but are not yet browned.
Stir in the potatoes and celery root. Add the stock and turn the heat up. As soon as the stock boils, reduce the heat to medium low and simmer for about 20 minutes, or until the potato and celery root cubes are completely tender.
While the soup simmers, slice the chard into thin strips. Prepare a plate with a layer of paper towels. Place the remaining tablespoon of olive oil into a skillet. Add the chard to the skillet and sauté for about 3-5 minutes, or until the chard become bright green and crispy. Transfer the chard to the paper towel-covered plate and set aside.
Transfer the soup to a blender or food processor in batches and puree until smooth. An immersion blender is easier and will also work. Add the milk or cream to the soup if you prefer a creamier soup. Season with salt and pepper and the cider vinegar to taste. Top each bowl of soup with the chard ribbons.
Optional note: I once added some apples to the broth (towards the end of cooking the celery root and potatoes). It turned out to be a great addition!