Bring 3 1/2 cups water, 1 cup of the evaporated milk, the macaroni, and 1/2 teaspoon salt to a simmer in a 12-inch nonstick skillet over high heat. Cook at a vigorous simmer, stirring often, until the macaroni is tender and the liquid has thickened, 9 to 12 minutes.

Whisk the remaining 1/2 cup evaporated milk, the cornstarch, mustard and hot sauce together in a small bowl, then stir into the skillet. Continue to simmer slightly thickened, about 1 minute.

Off the heat, stir in the cheddar and Monterey Jack, one handful at a time, adding water as needed to adjust the consistency of the sauce (I didn’t need any additional water when I made it). Stir in the butter and season with salt and pepper to taste. Serve immediately. Serves 4-6.