Step 1

Combine ingredients in the slow cooker: Coat the insert of a 3 1/2- to 4 1/2-quart slow cooker insert with cooking spray. Add the macaroni, whole milk, heavy cream, cream cheese, salt, mustard, and ground red pepper, if using. Stir to combine, making sure everything is evenly distributed. Smooth the top so the pasta is submerged.

Step 2

Cover and cook on LOW for 1 hour. Cover and cook on LOW for 1 hour.

Step 3

Stir the pasta. Working quickly so the slow cooker retains as much heat as possible, stir the pasta and cooking liquid, breaking up any large chunks of noodles.

Step 4

Cover and cook on LOW for 1 hour. Cover the slow cooker again and continue to cook for 45 minutes to 1 hour, or until pasta is tender.

Step 5

Stir the pasta and add the cheese. Again, work quickly to stir the pasta and cooking liquid to break up any clumps of pasta or cream cheese, especially around the edge and bottom of the slow cooker. Sprinkle the shredded cheese on top of the pasta and cooking liquid, but do not stir the cheese into the noodles.

Step 6

Cover and cook on LOW for 15 to 20 minutes. Cover and cook on LOW for 15 to 20 minutes. Use a fork to pluck out a noodle from under the cheese to see if it is plump and soft.

Step 7

Stir in the cheese and serve. Stir the warmed cheese into the cooked pasta and sauce. Lower the heat to WARM setting and serve macaroni and cheese straight from the slow cooker.