Spray a 4 quart slow cooker with nonstick cooking spray. In a small saucepan, heat the mustard, cornstarch, pepper, and evaporated milk until warmed through, whisking ocasionally. Stir in the cheese.

Pour the macaroni into the slow cooker. Top with the cheese mixture and stir. Cover and cook on low for 1-2 hours or on high 30 minutes.