I found this recipe on liquor.com.

gin, Lillet Blanc, creme de cacao, lemon juice

Oh, the rare pleasure of finding a cocktail with a clear history! This one was invented “in 1937 by a British bartender named C.A. Tuck, and named in honor of the celebrated 20th Century Limited train which ran between New York City and Chicago from 1902 until 1967. The recipe was first published in 1937 in the Café Royal Cocktail Book by William J Tarling, President of the United Kingdom Bartenders’ Guild and head bartender at the Café Royal.” – Wikipedia

I gotta get that Café Royal book.

The cocktail is delicious. I don’t think I’ve ever had a drink with Lillet Blanc that I didn’t like. Very lemon/citrus forward, with the botanical bite of gin and a whisper of chocolate. (Gosh, for someone who struggles to find the words to explain tastes, I feel like that one was pretty good.) This one goes on the “favorite” list, a list that doesn’t actually exist.