Cut the ends off your Swiss chard and set aside. Slice them finely along with your half onion.
In a large skillet, melt the butter and add onions plus Swiss chard ends (not the leaves), sautéing over low heat until the ends and onion soften, about 5 minutes.
While sautéing the ends and onions, slice the Swiss chard leaves into 1-inch thick strips.
Measure the remaining ingredients and set aside.
Add the strips of Swiss chard to your pan and stir.
Add the garlic, salt, and pepper.
Stir the Swiss chard until the chard starts to wilt, about 3 or more minutes.
Move the chard to the side of the pan. Add the flour to the center of the pan and stir a couple of times to cook all the flour.
Slowly pour in the 2% milk, then start stirring it all together while it thickens.
Add the nutmeg and cook until the sauce thickens.
Serve hot as a side dish.