Bring a large pot of salted water to a boil.
While the water is coming to a boil, thinly slice the garlic, chop the Calabrian chilis and chiffonade (slice into thin strips) or tear the basil by hand.
Place 2 tablespoons of the olive oil over medium-low heat. Once just shimmering, add the garlic, chilis, and a pinch of salt. If using red pepper flake instead of Calabrian chilis, add it at this stage.
Once the water is boiling, cook the pasta for 1 minute less than the box instructions (about 9 minutes is using spaghetti).
While the pasta is cooking, keep an eye on the garlic and chilis, stirring occasionally. The garlic is ready when it is softened and light golden brown but not crisp or burned.
When the pasta is cooked, add about ¼ cup of the pasta water to the pan with the garlic, oil, and chilis. Stir to emulsify. Add in the pasta and remaining olive oil and continue to stir.
Add the basil and stir together, ensuring the pasta is coated evenly with the sauce. Taste for seasoning and adjust if needed.
Plate the pasta. Add some freshly grated parmesan cheese and more fresh basil if desired.