Add the pancetta to a cold pan and cook slowly over a low heat until the fat renders and the pancetta is golden and crisp.
Cook the bucatini in well-salted boiling water until al dente.
Mix the egg yolks, Parmesan and plenty of black pepper in a bowl. Slowly whisk in around 2 tbsp of the hot pancetta fat.
Remove the pancetta from the pan, then add 2 tbsp of tomato paste. Cook for 4-5 minutes until darker, richer and slightly caramelised. Add chilli flakes here if using.
Turn off the heat and add the pasta straight into the pan with most of the pancetta.
Let it cool slightly, then add a splash of pasta water followed by the egg mixture. Toss until glossy, creamy and fully coated.
Finish with the remaining pancetta, extra Parmesan, black pepper and chives.
