Preheat your oven to 350°F (175°C).
Chop the cabbage into bite-sized pieces. Bring a large pot of water to a boil, add a bit of salt, and boil the cabbage for about 5–7 minutes until just tender. Drain well using a colander.
For extra flavor, you can lightly sauté the diced onion in a bit of butter or oil until translucent. (Or add it raw for a sharper bite.)
In a medium mixing bowl, combine the cream of chicken soup, mayonnaise (or sour cream), shredded cheddar cheese, diced onion, salt, and pepper. Stir well.
Place the cooked cabbage in a greased 9x13 inch baking dish. Pour the creamy mixture over the cabbage and stir to coat evenly.
In a small bowl, mix the crushed Ritz crackers with the melted butter. Spread the buttery cracker crumbs evenly over the casserole. Add a little extra cheese on top if you like it extra cheesy.
Bake uncovered for 30–35 minutes or until hot and bubbly and the top is golden brown.
Let it cool for a few minutes before serving. It pairs well with roasted meats, fried chicken, or as a standalone comfort meal.