Cook the box of mac and cheese to the package instructions. Put the mac and cheese back in the sauce pan and simmer for a minute so it is extra thick. Stir in the cheddar until it melts. You don't technically need the extra cheddar, but it helps the mac and cheese stay solid.
Pour the mac and cheese mixture onto a parchment lined baking sheet. Top with another piece of parchment and spread the mac and cheese out so it is about 3/4 of an inch thick. Refrigerate for at least an hour.
Remove the mac and cheese from the fridge and cut rounds of the pasta out with a cookie cutter.
Wrap a thin layer of beef around the pasta rounds.
Cook the burgers being careful not to overcook or the mac and cheese will explode out. Keep an eye on them, and once you start seeing the pasta leaking out, that's when you can pull them from the grill.
Serve on a bun with your favorite toppings. In this post, I used tomatoes with toasted breadcrumbs on top to mimic a classic baked mac and cheese.