Cook the spaghetti in boiling salted water according to the packet instructions. Meanwhile, cut the pancetta slices into 1cm (½in) lardons and lightly fry in a saute pan with the butter and a drizzle of oil. In a mixing bowl, whisk together the egg yolk, grated cheese and pepper.
Once the pasta is cooked, drain it and add it to the saute pan with a small ladle of the cooking water. Add another small ladle of pasta water to the bowl of egg yolk and mix it in until creamy.
Toss the spaghetti in the sauce, then add it to the mixing bowl with the eggs. Toss again until the sauce combines and become creamy enough to coat the pasta. The heat from the pasta will lightly cook the eggs.
Serve in a pasta bowl topped with the pancetta crisps broken on top as a garnish, followed by a sprinkle of Parmesan and a grating of black pepper.