Step 1: Heat olive oil in a large skillet or Dutch oven over medium-high heat. Add the Italian sausage, breaking it up with a spoon, and cook until browned and cooked through, about 5-7 minutes. Drain any excess fat, leaving about 1 tablespoon in the pan. Remove the cooked sausage to a plate and set aside.
Step 2: To the same skillet, add the diced onion and chopped swiss chard stems. Sauté for 3-5 minutes, until the onion softens and the chard stems are slightly tender. Season lightly with salt and pepper.
Step 3: Add the minced garlic to the skillet and cook for another minute until fragrant, being careful not to burn it.
Step 4: Return the cooked sausage to the skillet. Add the chopped swiss chard leaves, in batches if necessary, and pour in the chicken or vegetable broth. Stir everything together.
Step 5: Cover the skillet and cook for 5-7 minutes, or until the swiss chard leaves have wilted and are tender-crisp. Stir occasionally.
Step 6: Taste and adjust seasoning with salt and pepper as needed. Serve hot, garnished with grated Parmesan cheese if desired.