Preheat oven to 350°F and grease a 9x13-inch baking dish.
Bring a large pot of salted water to a boil. Add broccoli, cauliflower, and carrots and cook for 5 minutes until slightly tender but still crisp. Drain well and pat dry.
In a large bowl, combine cream of mushroom soup, sour cream, 1 1/2 cups of cheddar cheese, mayonnaise, garlic powder, onion powder, salt, and pepper. Mix until smooth.
Add the blanched vegetables to the cheese mixture and stir gently to coat all vegetables evenly.
Pour the vegetable mixture into the prepared baking dish and spread evenly. Top with remaining 1/2 cup cheddar cheese.
In a small bowl, mix crushed Ritz crackers with melted butter until crumbs are evenly coated. Sprinkle the buttery cracker mixture over the top of the casserole.
Bake uncovered for 30 minutes until bubbly around the edges and the cracker topping is golden brown.
Let stand for 5 minutes before serving.