Prepare the cabbage: Preheat the oven to 350°F (175°C). Chop the cabbage into bite-sized pieces and blanch in boiling water for about 3-5 minutes until slightly tender. Drain and set aside.

Sauté the onions: In a large skillet, melt 4 tablespoons of butter over medium heat. Add the chopped onions and cook until soft and translucent, about 5 minutes. Incorporate the blanched cabbage into the skillet and mix well. Season with salt and pepper.

Prepare the creamy mixture: In a mixing bowl, whisk together the condensed soup and mayonnaise. Pour this mixture over the cabbage and onion, stirring to combine.

Assemble the casserole: Grease a 9x13-inch baking dish with butter or non-stick spray. Transfer the cabbage mixture into the dish, spreading it out evenly.

Add the topping: In a small bowl, mix the crushed Ritz crackers with the remaining 3 tablespoons of melted butter. Sprinkle the shredded cheddar cheese over the cabbage mixture, then top with the buttered crackers.

Bake: Place the casserole in the preheated oven and bake for 25-30 minutes, or until the top is golden and bubbly.

Serve: Remove from the oven and allow the casserole to rest for a few minutes before serving. Enjoy the creamy, crunchy goodness!