2 slices white bread, roughly torn into nickel-sized pieces
225 grams thinly sliced deli ham, roughly chopped
Preheat your oven to 425ºF and lightly grease a nine inch square casserole dish with non-stick cooking spray or butter.
Bring a large pot of salted water to a boil then add the pasta and cook until al dente, about eight to 10 minutes. Drain the pasta and leave it in the colander or strainer until ready to use.
Meanwhile, melt the butter in a saucepan over medium heat. Add in the garlic and cook for about one minute then sprinkle in the flour. Whisk the flour in and cook, whisking constantly, for about one to two minutes to toast the flour. While continuing to whisk, slowly pour in the warm milk, salt, pepper, Herbes de Provence, and nutmeg and bring it all to a light boil. Cook, whisking frequently, until thick, about four to five minutes.
When the sauce is thick, turn the heat down to low and whisk in the mustard, Pecorino cheese, and two cups of the grated Gruyere. Switch to a heatproof spatula or a wooden spoon and carefully stir in the cooked rigatoni making sure that every noodle is well coated. Pour half of the mixture into your prepared casserole dish, scatter on half of the ham, then layer on the remaining pasta and ham and set aside.
To make the topping, whisk the egg and remaining two tablespoons of milk in a bowl. Season with salt and pepper and stir in the torn bread and remaining ½ cup of Gruyere.
Top the casserole with this bread mixture and pop it in the oven for 20 to 25 minutes or until golden brown and bubbly. Allow the mac and cheese to rest for a few minutes before digging in!