Heat the half & half in a medium skillet over medium/high heat. Watch as soon as it starts simmering, just before it reaches a boil, reduce the heat to low.

Starting with the american cheese, slowly stir the cheese in working in batches. Slowly increase the heat to medium, stirring constantly. And I do mean stirring constantly. As each addition of cheese is completely incorporate, smooth/bubbly, add a bit more and continue the process until all the cheese has been completely incorporated. 

Stir in the chilies, chili powder, nut meg, salt & pepper, and chili flakes until evenly incorporated.

At this point you have two options. A) Transfer the queso to a bowl or a small crock pot to keep it warm, and serve with chips. B) Transfer the queso to a small oven proof dish, and broil for 3 minutes, or just until it begins to bubble and brown.

Whichever method you choose, top the dish with diced tomato and cilantro leaves before serving and enjoy!