Pasta with Arugula and Walnuts

This recipe can be found on www.marthastewart.com. It was originally published in Everyday Food, April 2008. I love that it's simple and really healthful!

Prep: 10 minutes
Total: 25 minutes

Ingredients
Serves 4
12 ounces farfalle (bow-tie pasta)
Coarse salt and ground pepper
4 garlic cloves, thinly sliced
4 tablespoons butter (or olive oil for a vegan option)
1 pound baby arugula (or a mixture of arugula and baby spinach)
1 can (15 ounces) cannellini beans, rinsed and drained
1/3 cup walnut pieces, toasted

Directions
Cook pasta in a large pot of boiling salted water until al dente. Reserve 1/2 cup pasta water; drain pasta, and set aside.
Place pasta pot over medium heat. Add garlic and 1 tablespoon butter; cook, stirring, until garlic is fragrant, about 2 minutes.
Add arugula to pot; toss just until wilted. Add beans, pasta, and remaining 3 tablespoons butter; season with salt and pepper. Toss, adding enough reserved water to mixture to coat pasta. Alternatively, you can add milk or almond or rice milk for a creamier texture. Garnish with toasted walnuts.