Spaghetti with Arugula & Clam Sauce

Bring a large pot of water to a boil. Cook pasta according to package directions. Drain.

Meanwhile, heat oil in a large skillet over medium heat. Add onion and cook until starting to soften, about 2 minutes. Add garlic and crushed red pepper and cook, stirring, until fragrant, about 1 minute. Add clams and their juice, wine, lemon zest and lemon juice. Bring to a simmer. Adjust heat to maintain a simmer and cook, stirring occasionally, until reduced by half, 6 to 8 minutes.

Stir in butter and salt. Add the hot pasta and toss to coat. Add arugula and toss until slightly wilted, about 1 minute. Serve with Parmesan, if desired.