I have not seen a modern recipe for this sauce, and the original gave no indication as to what foods should be served with it. I decided to test it with a mild-flavored fish, but it would be fine for any light-flavored meat, as well.
Place the stock, wine, lemon slices, cloves, bay leaf, parsley sprigs, and onions in a saucepan over medium heat and bring to a boil. Reduce the heat and simmer until reduced and more sauce-like, about 90 minutes.
Strain the sauce and discard the solids. Return the liquid to a clean saucepan and reheat. Season with salt and add some pepper. Add the egg yolk, minced parsley, and serve