The Amaretto Sour is thought to have first originated in the 1970s as a promotional push from liqueur brand Disaronno, then known as Amaretto di Saronno. It’s a take on the classic sour template of drink those that include a spirit combined with sweet and sour elements—that’s unique for a few reasons.

While most sours use a base spirit paired with syrup or a liqueur for sweetness, balanced with fresh lemon or lime juice, the original Amaretto sour only required two ingredients: amaretto and lemon juice.

Référence : https://www.liquor.com/recipes/amaretto-sour/

The cocktail was introduced to the public in 1974, devised by the importer of Amaretto di Saronno as a simple mix of two parts amaretto liqueur to one part lemon juice. It became a popular cocktail in the 1980s; most bartenders at the time substituted commercial sour mix for the lemon juice. The drink was popular as a one-dimensional easy-drinking cocktail, flavored mostly by the base spirit used.^[3]

Référence : https://en.wikipedia.org/wiki/Amaretto_sour#:~:text=as%20a%20garnish.-,History,mix%20for%20the%20lemon%20juice.

Référence : https://www.diffordsguide.com/cocktails/recipe/53/amaretto-sour