Tetrazzini sauce is commonly flavored with sherry, a fortified wine.
Tetrazzini is an Italian-American baked pasta dish usually made with poultry or seafood, mushrooms, and pasta such as spaghetti, linguine, or egg noodles. Its creamy sauce commonly combines butter, milk or cream, cheese, and sherry. Some versions use béchamel, Mornay sauce, or condensed cream soup instead.
The dish is named after Luisa Tetrazzini, an acclaimed Italian opera soprano who became famous in the United States. Despite the name, tetrazzini is not a traditional Italian dish; its exact American origin is disputed, with competing claims from restaurants in San Francisco and New York.
Sherry is the key distinction in this question because it is fortified after fermentation. White wine may also flavor tetrazzini, but it is not normally classified as a fortified wine. Port and marsala are fortified wines too, yet they are not the conventional answer for the classic sauce.