Pasta with Red Pesto

Directions

1. 1
   In a small sauce pan, combine the olive oil, walnuts, anchovies and garlic. Cook over medium heat, stirring often, until walnuts and garlic are fragrant and lightly browned, about 5 minutes.
2. 2
   Add tomato paste and cook, stirring constantly, for 1 minute.
3. 3
   Transfer to a small bowl and let cool for 5 minutes.
4. 4
   Combine the olive oil mixture, Parmesan cheese, chiles, lemon juice and salt in a food processor. Purée until smooth.
5. 5
   Bring a large pot of salted water to a boil. Cook pasta until al dente according to package directions.
6. 6
   Drain, reserving 1 cup cooking liquid, and transfer to a large bowl.
7. 7
   Add ⅓ cup reserved cooking liquid, butter and pesto to pasta and stir vigorously until combined. If necessary, add more reserved cooking liquid to loosen the sauce. Season with additional salt to taste. Top with chili flakes, if using.