Form 1.5 inch balls with the cold mac and cheese, pressing to make them compact. Lay them on a sheet pan and put it back in the fridge while you prepare the rest of the ingredients. Note: they need to stay a bit cold (but not frozen) so they retain their shape well.
Prepare your breading station: In a shallow bowl, add the flour. Then, in a second shallow bowl, whisk the eggs. In a third shallow bowl, combine the panko bread crumbs, Italian bread crumbs, and 1 teaspoon salt. Set aside.
Get the oil ready: Heat the vegetable oil (3 to 4 inches deep, or enough for the mac and cheese bites to fully submerge) in a deep large Dutch oven until the oil’s temperature reaches 360 to 375 degrees F. Tip: Use a candy thermometer to measure the oil’s temperature.
While the oil is heating, assemble the mac and cheese bites: coat each ball in flour first, then the whisked eggs, and then the bread crumb mixture. Press slightly to make sure the bread crumbs adhere well.
Deep fry: Fry in small batches for about 3 minutes or until evenly golden brown. Tip: every time you add food into the oil, the temperature drops. Increase the heat to get it back closer to 360-375 degrees F.
Transfer to a large plate lined with paper towel to drain excess oil. Serve immediately. Enjoy!