Step 1

In a medium saucepan over low heat, add the milk, garlic, and black pepper. Whisk to combine and infuse the milk, whisking occasionally, until it's warm and steaming but not boiling, about 10 minutes.

Step 2

In a large saucepan, melt the butter until sizzling over medium heat. Whisk in the flour and cook for a minute. Slowly pour in the hot milk mixture, whisking to avoid any lumps. Cook over medium-low heat, whisking frequently, until slightly thickened, 4 to 6 minutes. Remove and discard garlic. Whisk in the Pecorino Romano and salt until cheese has melted. Transfer to a medium bowl and press plastic wrap directly onto surface of sauce; refrigerate until completely cooled. (It will thicken as it cools.)

Step 3

Preheat the oven to 375°. Grease a 9-by-13-inch baking dish or 4-quart baking dish. Ladle about 1 cup of sauce in the bottom of the dish, spreading to create an even layer. Lay 2 half sheets of pasta together, overlapping slightly, to create one long vertical strip. Spread about 2 tbsp. of cooled sauce on the strip, then sprinkle with 2 tbsp. mozzarella. Gently roll up both pasta sheets into a tight spiral and place the roll, seam-side down, in the prepared dish. Repeat the process with the remaining pasta sheets. Top the rolls with the remaining sauce and mozzarella. Garnish with additional grated Pecorino Romano and more cracked black pepper.

Step 4

Cover the baking dish with parchment paper and then cover tightly with a sheet of aluminum foil. Bake on the middle rack for 45 minutes, until cheese is melted and sauce is bubbling. Remove the foil and parchment paper and increase the oven temperature to 400°; bake for an additional 20 minutes or until the top is golden. Allow to set for 5 minutes before serving.