Galliano
A golden Italian herbal liqueur flavored with vanilla, anise, and a blend of other herbs and spices, sweeter and more syrupy than a plain spirit like vodka or bourbon. Best known as the defining flavor in a Harvey Wallbanger cocktail, where its vanilla-anise sweetness plays against orange juice and vodka -- the same combination this cake borrows.
Buying guidance
It's a specialty bottle most liquor stores carry only one version of, sold in a distinctive tall bottle -- there isn't a "cooking grade" vs. "sipping grade" tier to choose between the way there is with tequila or bourbon. A little goes a long way given how assertive the anise-vanilla flavor is, so the smallest available bottle size is often enough unless it's used often.
Substitutions
- Sambuca or another anise-forward liqueur -- shares the licorice note but is thinner and lacks Galliano's vanilla sweetness.
- Vanilla extract plus a splash of any neutral spirit -- approximates the vanilla side of the flavor while dropping the anise character entirely.
- Omit entirely -- a drink or cake loses its distinctive Harvey Wallbanger flavor but still works structurally with the vodka and orange juice alone.
Tips & common mistakes
Its sweetness and syrupy body make it easy to mistake for a smaller quantity than it is when measuring by eye -- an overpour reads as noticeably more anise-forward than intended, so measure it the same as any other liqueur rather than free-pouring.
Storage
Keeps for a long time at room temperature away from direct light, whether opened or unopened -- like other liqueurs, it doesn't need refrigeration, though its flavor can fade gradually over a year or more once opened.