Cook the fettuccine in plenty of salted boiling water.
Put a steel bowl on a saucepan to cook in a bain-marie (make sure that the bowl is not in direct contact with the water but only receives the heat of the steam). Put all the ingredients in the bowl and stir with a whisk until the mixture becomes creamy (about 5 minutes). Then, remove the bowl from the heat and continue mixing for a couple of minutes.
Drain the pasta and season it with the Pecorino Toscano DOP flavored zabaione. If you like it, garnish with toasted bacon and serve hot.