Preheat the oven to 350°F. Grease a 13x9-inch or 3.5 to 4-quart baking dish with butter or non-stick cooking spray. Set the dish aside.
Slice the cabbage into 1-inch pieces with a sharp knife.
Melt 2 tablespoons of butter in a large skillet over medium heat. Add the cabbage and cook, stirring occasionally, until tender, for about 10 to 12 minutes.
Add cubes of Velveeta cheese, sugar, seasoned salt, and crushed red pepper flakes. Gently fold until the cheese is melted.
Transfer the cabbage mixture to the prepared baking dish.
Melt the remaining 4 tablespoons of butter in a small bowl. Mix the melted butter with the crushed crackers. Evenly sprinkle the mixture over the casserole top.
Bake for 20 to 25 minutes, until the top turns golden brown and the casserole bubbles at the edges.
Remove the dish from the oven and allow it to cool briefly. Garnish with chopped parsley or sliced green onions as desired.