Fill a large saucepan with water, season generously with salt, and bring it to a rolling boil.

Add the pasta and cook for 8-10 minutes, or according to package directions, until al dente; drain, reserving 1 cup of pasta water, and set aside.

Meanwhile, melt the butter in a large frying pan or skillet over medium heat.

Add the chopped garlic and cook, stirring occasionally, for 1 minute until fragrant but not browned.

Sprinkle in the all-purpose flour and cook, stirring constantly, for 1 minute until a thick paste (roux) forms and the raw flour smell disappears.

Gradually whisk in the milk, a little at a time, until smooth; stir in the ground black pepper and a pinch of salt.

Bring the sauce to a gentle boil, then reduce heat to low and simmer for 3-4 minutes, stirring occasionally, until the sauce thickens and coats the back of a spoon.

Add the cooked pasta, grated Parmesan cheese, and chopped fresh basil to the sauce; stir until everything is well combined and heated through.

Serve immediately, garnished with additional fresh basil leaves and dried red chili flakes if desired.