Cook the pasta according to the package directions. Reserve ½ cup of the cooking water. Drain the pasta and return it to the pot.
Meanwhile, heat the oil in a large nonstick skillet over medium heat.
Add the potatoes, ¾ teaspoon salt, and ¼ teaspoon pepper. Cook, covered, stirring occasionally, for 10 minutes.
Add the shallots and rosemary. Cook, uncovered, stirring occasionally, until the potatoes are tender, 3 to 5 minutes.
Toss the pasta with the potato mixture, Parmesan, and reserved cooking water. Dollop with the ricotta before serving.