Combine all ingredients except Ritz crackers in a large bowl. Mix well. Pour into 13x9 inch pan. Cover with foil and bake at 350°F for 50 minutes.
Remove foil and sprinkle crushed Ritz crackers on top of casserole.
Bake, uncovered, for an additional 10 minutes or until crackers are golden brown. Let sit for 10 minutes before serving.