Heat oven to 350°F. Spray 12 regular-size muffin cups with cooking spray. Cook macaroni as directed on package—except cook 2 minutes less time. Drain; place in large bowl.
Meanwhile, in 10-inch skillet, cook ground beef over medium-high heat 5 to 7 minutes, stirring occasionally, until thoroughly cooked. Drain; set aside.
In microwavable bowl, microwave butter, milk and prepared cheese product on High about 5 minutes. Remove from microwave; stir with whisk until cheese begins to melt. Microwave on High in 1-minute increments, stirring after each minute, until cheese is completely melted and mixture is smooth.
Add cheese mixture and ground beef to macaroni in bowl. Stir in 1 1/2 cups of the shredded cheese until well mixed. Add salt and pepper to taste.
Fill each muffin cup with macaroni mixture. Sprinkle bread crumbs and remaining shredded cheese over tops.
Cover pan loosely with foil, making sure foil does not touch cheese. Bake 20 minutes.
Remove from oven; remove foil. Cool at least 10 minutes before remove muffins from cups.