Add the lemon zest, olive oil, and salt, then top with the boiling water.
Bring to a boil and simmer for 8 minutes, stirring occasionally.
Stir in the lemon juice, butter, and cheese, and toss well. If it is not glossy, add a splash of water.
Serve with pepper and chili flakes for the adults, and chop for the kids.
Notes
Use freshly grated Parmesan or pecorino for the glossiest sauce. Reserve a splash of the starchy cooking water to loosen it if needed. Leave out the chili flakes to keep it kid-friendly.