Start by preparing the garlic and basil.
Bring a large saucepan of lightly salted water to a rolling boil.
Add the 15 peeled garlic cloves and cook for 8 minutes until softened. Use a slotted spoon to transfer the garlic directly to a blender or food processor.
Add 1/3 cup (720 ml) of the basil leaves to the same boiling water and blanch for just 5 seconds—this keeps the color vibrant! Immediately remove the basil with the slotted spoon, drain well on paper towels, and add it to the blender with the garlic.
Keep the water boiling for the pasta.
Cook the pasta in the reserved boiling water according to the package directions until al dente.
Before draining, carefully ladle out and reserve 1/2 cup (480 ml) of the starchy pasta water.
Drain the pasta and return it to the warm pot.
Cover to keep it warm while you finish the pesto.
While the pasta cooks, make the pesto. To the blender with the garlic and basil, add the olive oil, 2 tablespoons (30 ml / 1 fl oz) of the toasted pine nuts, 2 tablespoons (30 ml / 1 fl oz) of the Pecorino Romano cheese, the sea salt, and black pepper.
Cover and blend until the mixture is nearly smooth. The pesto will be a bit thin, which is perfect for coating the pasta.
Pour the freshly blended pesto over the warm pasta in the pot.
Toss gently to coat every nook and cranny. If the sauce seems too thick, add a splash of the reserved pasta water at a time until it reaches a silky, saucy consistency.
Transfer the pesto pasta to a large serving bowl.
Garnish generously with the remaining 1 cup (240 ml) of fresh basil leaves, the remaining 1/4 cup (960 ml) of Pecorino Romano cheese, and the rest of the toasted pine nuts.
Serve immediately and enjoy!
Don't skip toasting the pine nuts! It takes just a few minutes in a dry skillet over medium heat and unlocks a deep, nutty flavor that makes a huge difference.