Preheat your oven to 325°F (163°C). Lightly grease a 2-quart baking dish with butter or nonstick spray to prevent sticking.

Bring a large pot of water to a boil and add a generous pinch of salt. Add the dry ziti pasta and cook until al dente, according to package instructions. Drain the pasta, but do not rinse; set it aside.

While the pasta is boiling, shred both the extra-sharp cheddar and Monterey Jack cheeses. Combine the shredded cheeses in a bowl and set aside. I prefer shredding cheese from blocks rather than buying pre-shredded—it melts so much better.

In the prepared baking dish, layer one third of the cooked ziti pasta (from Step 2), one third of the combined shredded cheeses (from Step 3), and half of the sliced salted butter. Repeat these layers, finishing with a layer of cheese on top. Gently press the mixture down into the baking dish to compact slightly.

In a bowl, beat together the egg and whole milk until smooth. Slowly pour the mixture evenly over the layered casserole, making sure to cover as much surface as possible so the egg and milk will soak in.

Bake the casserole at 325°F (163°C) for 45 minutes to 1 hour, or until the top is golden brown, bubbly, and the milk mixture is set. For an extra golden top, I sometimes broil the casserole for the last 2 minutes—just keep a close eye to avoid burning.