
Hazelnut liqueur is a sweet liqueur flavored with roasted hazelnut, often with vanilla, cocoa or coffee notes.
Nut sweetness is easy to find and this particular nut is not, so a swap changes which nut rather than whether there is one. Watch the strength: nut syrups bring the flavor without the alcohol, and topping it back up with neutral spirit keeps the drink where it was.
Amaretto / almond liqueur
Amaretto reads as marzipan rather than roasted nut. The drink turns sweeter and more kernel-like: pull the sugar back by about a third, and nothing will bring the toasted note back.
Sugar and alcohol both preserve it, so an opened bottle keeps for years and quietly loses its top aroma. House-made infusions are another matter: the nut oil goes rancid, and that is what limits them to a couple of months — not the sugar.