Cook pasta according to packet instructions.
Fry bacon.
Once pasta is cooked, strain and return to pot.
Add cream, bacon and parmesan. Return to heat, stirring, until cheese melts.
Remove from heat and immediately stir through the egg yolk. The heat of the pasta should cook the yolk, but don't return to heat or it will overcook.
Sprinkle with a little extra parmesan to serve.