Cook macaroni one minute less than indicated for al dente. Drain.
Melt butter, add flour and whisk together to form a roux. Add milk, Dijon mustard and sour cream, stirring frequently, until thickened. Remove from heat.
Brush olive oil onto interior surface of crock pot or use a non-stick spray.
Put macaroni in bottom of crock pot followed by the roux mixture. Stir to combine.
Add 2 cups of shredded cheese of your choice. Stir just enough to distribute cheese within macaroni/roux mixture. Grind fresh black pepper over mixture.
Place block of light cream cheese in middle. Cover with the remaining 2 cups of cheese.
Place lid on top and set crock pot to low for no more than 1 1/2 hours.
Turn off and remove lid. Stir gently to combine and evenly distribute cheeses. Serve it up!