Rinse the Swiss chard well to remove grit. Separate stems from leaves. Thinly slice the stems into 1/4-inch pieces. Stack the leaves, roll them tightly and slice crosswise into 1-inch ribbons. Pat dry or shake off excess water.

Saute onions

Heat 2 tablespoons olive oil in a large skillet over medium heat until shimmering. Add the thinly sliced onion and a pinch (about 1/4 tsp) of salt. Saute, stirring occasionally, until soft and translucent, about 6–8 minutes.

Cook the stems

Add the sliced chard stems to the skillet and cook, stirring, for 3–4 minutes until they begin to soften and take on a little color.

Add garlic and leaves

Push stems and onions to the side, add the minced garlic and red pepper flakes, and cook 30–45 seconds until fragrant. Add the chard leaves in batches, letting each batch wilt down slightly before adding more so everything fits in the pan.

Deglaze and simmer

Pour the 1 tablespoon white wine (or vegetable broth) into the pan to deglaze, scraping any browned bits with a wooden spoon. Add 1 tablespoon vegetable broth (or water), cover the pan, reduce heat to medium-low and steam for 3–4 minutes until leaves are tender but still bright green.

Flavor builders and seasoning

Uncover, increase heat to medium, and cook off any remaining liquid for 1–2 minutes. Season with 2 3/4 teaspoons kosher salt (adjust to taste) and 1 teaspoon freshly ground black pepper. Stir in lemon zest and squeeze the lemon juice over the chard, tossing to combine.

Optional finishing ingredients

If using, sprinkle the toasted pine nuts (or walnuts) over the chard and toss. Remove from heat and grate 2 tablespoons Pecorino Romano or Parmesan over the top. Finish with a drizzle (about 1 teaspoon) of extra-virgin olive oil if desired. Taste and adjust salt, pepper, or lemon.

Serve warm as a side, tossed with pasta, or spooned over toasted bread. Leftovers keep in an airtight container in the refrigerator for up to 3 days.