How to Make It
Cook pasta according to package directions for al dente, omitting salt and fat. Drain in a colander over a bowl, reserving 1 cup cooking liquid.
While pasta cooks, heat walnut oil in a large skillet over medium-high. Add garlic and cook, stirring often, until golden, 3 to 4 minutes. Stir in parsley; remove from heat. Let oil mixture cool 2 minutes.
Add 1/2 cup reserved cooking liquid to oil mixture, and return to medium-high heat. Cook until sauce has reduced by half, about 5 minutes. Stir in cooked pasta. Add 1/4 cup reserved cooking liquid and cook, stirring constantly, until sauce has thickened, about 2 minutes. Stir in remaining 1/4 cup cooking liquid as needed to reach desired consistency. Season with salt; if desired, top with cheese and black pepper. Serve immediately.