Penne with Asparagus & Lemon Cream Sauce

Put a large pot of lightly salted water on to boil. Heat oil in a large skillet over medium heat. Add asparagus and scallions and cook, stirring occasionally, until the vegetables are tender and browned in places, 10 to 12 minutes. Meanwhile, whisk ricotta and lemon zest in a large bowl. Cook penne until just tender, about 10 minutes. Measure out 1/4 cup of the pasta-cooking water; stir into ricotta mixture until creamy. Drain the penne and mix into the ricotta mixture; toss to coat. Add the vegetables and toss well. Season with salt and pepper. Serve, garnished with basil.