Preheat oven to 350°F. Butter or spritz with non-stick spray a 13"x9" or 3.5-4 quart baking dish. Set aside.
Using a sharp knife, slice and cut the cabbage in 1-inch pieces.
In a large skillet, melt 2 tablespoons of the butter over medium heat. Add cabbage and cook stirring occasionally until tender, about 10-12 minutes.
Add Velveeta cheese cubes, sugar, seasoning salt, and crushed red pepper flakes. Gently fold the mixture until the cheese has melted.
Transfer the cabbage mixture to the prepared baking dish
In a small bowl, melt the remaining 4 tablespoons of butter. Combine the melted butter with the crushed crackers. Sprinkle the mixture evenly over the top of the casserole.
Bake for 20-25 minutes, or until the top is golden brown and the casserole is bubbling around the edges.
Remove from the oven and let it cool for a few minutes before serving. Garnish with chopped parsley or sliced green onion if desired.