How to Make It
Cook the pasta according to the package directions, reserving ¾ cup of the cooking water; drain the pasta and return it to the pot.
Meanwhile, heat oven to 450° F. Toss the potatoes, oil, ¾ teaspoon salt, and ¼ teaspoon pepper on a rimmed baking sheet and roast for 10 minutes.
Add the cabbage to the potatoes, toss to combine, return to oven, and roast until the potatoes and cabbage are tender and beginning to brown, 12 to 15 minutes more.
Add the potato mixture, fontina, and ½ cup of the reserved cooking water to the pasta and toss to coat (adding more cooking water as needed to loosen the sauce).