Prepare the bacon by cutting it into small pieces, slice the onion thinly, separate the egg yolk, and chop fresh parsley if available.

Boil 1L of water with 10g of salt, then cook the spaghetti according to the package instructions. Drain and set aside.

Heat olive oil in a pan, add bacon and onion, and cook until the onion becomes translucent. Add heavy cream and milk, then bring to a simmer.

Once the sauce thickens slightly, turn off the heat and quickly stir in the egg yolk to avoid curdling. Add Parmesan cheese and parsley, then mix well.