Step 1

Place 1/4 cup walnut halves or pieces into a small skillet. Place over medium heat. Stir, toss, and shake the nuts a few times as the skillet heats up and continue to do so until the nuts are golden-brown and toasted, 4 to 7 minutes. Transfer to the bowl of a food processor fitted with the blade attachment.

Step 2

Bring a large pot of salted water to a boil. Meanwhile, make the pesto.

Step 3

Finely grate 1 ounce Parmesan cheese (about 1/2 packed cup) or measure out 1/3 cup store-bought grated. Pick the leaves and tender stems from 1/2 medium bunch fresh parsley until you have 1/2 packed cup.

Step 4

Smash and peel 1 garlic clove. Add the garlic to the food processor and pulse until coarsely chopped, about 6 pulses. Add the Parmesan, parsley, 1 (8.5-ounce) jar sun-dried tomatoes with their oil, 1/4 teaspoon balsamic vinegar, and 1/4 teaspoon kosher salt to the food processor. Pulse, scraping down the sides of the bowl occasionally, until a coarse paste forms, 20 to 25 pulses. (Makes 1 1/4 cups pesto.)

Step 5

Add 1 pound dried penne pasta to the boiling water and cook according to package directions until al dente, 10 to 11 minutes. Reserve 1/2 cup of the cooking water. Drain the pasta.

Step 6

Return the pasta to the now-empty pot. Off the heat, add the sun-dried tomato pesto and toss until the pasta is evenly coated, adding 1 tablespoon of pasta water at a time as needed if the pasta seems dry . Serve topped with more grated Parmesan cheese and red pepper flakes if desired.