Cook the pasta

• Bring a large pot of salted water to a boil.
• Cook the spaghetti until al dente.

Prepare the lemon mixture

• Zest the lemon and squeeze its juice into a bowl.
• Add the grated Parmesan and freshly ground black pepper and mix into a paste.

Emulsify the sauce

• Melt the butter with the olive oil in a pan over low heat.
• Add the lemon and Parmesan mixture and a splash of pasta water.
• Stir until smooth and creamy.

Combine and serve

• Drain the spaghetti, keeping some pasta water.
• Toss the pasta in the lemon sauce, loosening with pasta water if needed.
• Serve immediately with extra Parmesan and pepper.