Arugula Hazelnut Pesto

• 2 cups arugula, washed and dried
• 1 cup parsley, washed and dried, stems removed
• 2 cloves chopped garlic
• ¼ cup lightly roasted hazelnuts
• zest and juice of half a lemon
• salt to taste
• 1 cup extra-virgin olive oil
• 20 ounces linguine
• 4 tablespoons butter, softened to room temperature
• ½ cup grated or shaved Parmigiano-Reggiano or Grana Padano or other hard cheese

Put arugula, parsley, garlic, hazelnuts, lemon zest, lemon juice, an ample pinch of salt, and ¼ cup olive oil in a food processor and process slowly. Gradually add the remaining olive oil until pesto reaches a uniform, creamy consistency. Cook linguine in salted water until al dente, and then drain, reserving some of the water. Toss linguine with the pesto, butter, and a little of the reserved water to thin the sauce. Serve topped with cheese.