Heat 1 tablespoon of butter in a large skillet over medium heat. Add the sliced onions, salt and pepper to the skillet and sauté until starting to soften, about 5 minutes.
Add the garlic to the skillet and cook for an additional 1-2 minutes until fragrant.
Add the chopped Swiss chard stems to the skillet and cook until softened, about 5-8 minutes.
Once the stems are softened, add the chopped Swiss chard leaves to the skillet. Cook the Swiss chard leaves until wilted, stirring occasionally, about 2 minutes.
Once the Swiss chard is cooked to your desired doneness, stir in the remaining ½ tablespoon of butter until melted. Sprinkle with shredded Parmesan and keep over the heat for about 30 seconds to let it soften and get slightly melty.
Serve.
Notes
LeftoversStore in an airtight container in the refrigerator for up 4 days. I don't recommend freezing as the chard will release extra moisture when thawing which will affect the texture.Sauté leftovers in a pan over medium low heat (with a little extra butter) for 3-5 minutes until heated through or warm in the microwave.