Defrutum is a reduced grape must used in ancient Roman cooking. If unavailable, you can substitute with a mixture of grape juice reduced by half or a blend of honey and balsamic vinegar.
Liebstoeckl, also known as mugwort, has a distinct bitter and aromatic flavor. Use sparingly as it can be overpowering. Rue is also quite bitter; ensure you use the correct amount for balance.
This recipe is based on Apicius, Book 9, Recipe 10, a historical source for ancient Roman cuisine.