Finishing pasta in its sauce helps the sauce coat each piece instead of sitting separately in the bowl. A little starchy cooking water loosens the mixture and can help oil and liquid come together. Add it gradually so you keep control of the final consistency.
Step by step
Have the sauce ready
Use a pan large enough to hold the pasta and sauce together without spilling. Bring the sauce to the heat the recipe needs while the pasta cooks. Keep delicate cheese or egg additions for their specified later stage.
Move the pasta before it is too soft
Reserve some cooking water in a heatproof jug. Transfer the pasta when it is slightly firmer than the intended final texture, allowing for the extra cooking in the sauce.
Stir with a small splash of water
Add a little reserved water and stir, fold or toss carefully. Keep the pasta moving so sauce reaches all surfaces. Add more water only when the pan looks dry or the coating becomes too thick.
Check the texture and serve
Stop when the pasta is cooked as intended and the sauce clings without a large watery pool. Complete any off-heat additions, then serve promptly. Pasta continues absorbing liquid as it stands.
Greasy, watery or clumped sauce
A greasy sauce may need a little cooking water and more mixing, not simply more oil. Excess water needs gentle reduction if the pasta can tolerate more cooking. Cheese and egg sauces can clump or curdle over strong heat, so follow their temperature sequence instead of boiling every sauce together.
