Pick the basil leaves from the stalks, reserving the smaller top leaves for decoration.
Finely grate around 20g of Parmesan cheese.
As the pasta timer nears completion, the sauce should have thickened to a jam-like consistency.
Once the spaghetti is al dente, take it off the heat and use tongs to lift it straight into the pan of sauce. A little pasta water coming with it is fine.
Turn up the heat under the pan, add basil leaves, and shake/stir to coat the pasta.
Add a bit more pasta water to achieve a lightly soupy consistency in the sauce.
Fry the pasta for 1-2 minutes, tossing or stirring, until the water is mostly absorbed, and the pasta is cooked.
If needed, add more water and cover the pan with a lid to help the pasta finish cooking.
Take out the garlic clove from the sauce.
Turn off the heat and add the finely grated Parmesan cheese to the pan, stirring to create a creamy sauce.
If the pasta stiffens, add a dash more pasta water to maintain the desired consistency.
Taste for seasoning and adjust if necessary.