From: Rabbi Moshe Sofer
To: Rabbi Wolf Chayes
The question is whether a secondary food's own condiment (tafel of a tafel) is covered by an original blessing—specifically whether charoses dipped with maror is exempted at the Seder, and whether sugar in coffee is covered by a blessing on wine during a meal. The Chasam Sofer proves from Berachos 35b that the tafel-of-a-tafel principle applies universally, even when the exemption chain is based on a food's status rather than direct necessity.
Source: Shu"t Chasam Sofer OC §47