Swiss Chard is called “Acelgas” in Mexico, and are often used as part of vegetable soups, stews, and tamales. The variety found in Mexico has large green leaves and sometimes is included in the prepackaged vegetable mix sold at the markets.
Peel and dice the potato, place in a medium saucepan, cover with cold water and cook on a medium heat. Bring to a boil, an reduce to simmer. Precook for about 10 to 15 minutes. Do not over cook since the potatoes will finish cooking with the rest of the soup ingredients in the final step.
While potatoes cook, cut the Swiss Chard, first cutting the stalk and then cutting the leaves into 2-inches pieces.
In a large saucepan, heat oil over a medium heat. Add onion and cook until transparent. About 2-3 minutes. Add the garlic and keep cooking for 2 more minutes, onion will look slightly browned.
Add chopped tomato and cook for 5 minutes, the tomatoes will release their juices. Keep stirring while cooking.
Add potatoes and cook for 2 more minutes. Then stir in the chicken broth and Swiss chard leaves. Season with salt and pepper. Reduce heat and simmer, partially covered with the saucepan lid, for about 15 minutes and until vegetables are tender.