Swap Swiss cheese for mozzarella, provolone, or a mild cheddar if that’s what you have on hand; just avoid very sharp cheeses that can overpower the gentle onion flavor. For a little crunch, uncover the casserole for the last 10 minutes of baking and sprinkle 1/2 cup crushed butter crackers or French-fried onions over the top.
If you prefer a lighter version, use light sour cream and reduce the cheese to 3/4 cup, understanding it will be a bit less rich but still comforting. Leftovers reheat
