1 1/2 to 2 pounds very lean ground beef
1/2 cup finely chopped onion
1 lg. onion, chopped fine
2 pounds Velveeta cheese, cut in small cubes or shredded
1 lg. jar Old El Paso taco sauce or Rotel tomatoes with green chile peppers

In a large skillet, brown ground beef and onion, breaking up ground beef with a spoon, until onion is tender and beef is no longer pink. Drain well. Mix all together in crockpot. Cover and cook on LOW for 2 to 3 hours, until cheese is melted.