Cook pasta al dente in a large stockpot of generously-salted water according to package instructions.

While pasta is cooking, heat olive oil (or melt the butter) in a saute pan over medium-high heat. Add the sliced garlic and cook for 2-3 minutes, or until it begins to turn just slightly golden. Remove from heat.  (And if the pasta is not yet ready, transfer the garlic to a separate dish to prevent it from overcooking.)

Once the pasta is cooked, drain it. Then immediately stir in the garlic and olive oil mixture, arugula, and Parmesan cheese.  Toss until combined.

Serve immediately, topped with extra Parmesan cheese (and toasted pine nuts, if using).