In a saucepan, melt butter until it sizzles. Stir in flour, salt and pepper. Over medium heat, add heavy cream and stir constantly until thickened (about 5-7 minutes).
Reduce heat to low. Stir in shredded cheeses. Stir constantly until cheese is melted.
Add cooked macaroni to cheese mixture and stir well coating pasta.
Burger
In a bowl, mix ground beef with salt and pepper. Form into 2 patties.
Place the burgers on a hot propane grill and cook for 3-5 minutes and then flip and cook for another 3-5 minutes on the other side, until desired level of doneness has been achieved.
Layer a cheddar cheese slice on top of each burger during the last few minutes of cooking and cook until the cheese melts.
Place one burger patty onto the bottom bun. Add a generous portion of the mac n cheese onto the burger. Add any additional toppings you'd like (onions, bacon, lettuce, tomato, etc.) and place the top of the bun on the burger. Enjoy!