Step 1Bring a large pot of generously salted water to a boil.
Step 2Meanwhile, heat 2 tablespoons oil in a large skillet over medium heat. Add the garlic and cook, stirring often, until light golden, about 1 minute. Add the pine nuts, capers and a pinch or two of chile flakes, if using, and season with 1/4 teaspoon salt. Cook, stirring, until the nuts are toasted, about 3 minutes. Remove the pan from the heat.
Step 3Once the water is boiling, add the pasta and cook until al dente. (Taste a noodle after 5 minutes and again every minute thereafter. The pasta is done when it tastes soft but still has a pleasantly chewy resistance when you bite down.)
Step 4Reserve about 1 cup of the pasta cooking water, then drain the pasta. Transfer the noodles directly to the skillet, set it over medium-high heat, and add about three-quarters of the reserved water and the remaining 3 tablespoons oil. Cook, stirring often, until the sauce coats the noodles, 1 to 2 minutes. There should be a little sauce pooling at the bottom of the skillet; if there is not, add more cooking water and stir well. Season with more salt and pepper, if you like, and serve hot.