An amaretto sour is a sweet, zesty cocktail with a light almond flavor. A basic blend of amaretto, lemon juice and simple syrup, it is typically served over ice and garnished with a wedge of lemon or a few maraschino cherries. You can make an amaretto sour with margarita mix if you don't have any regular sweet-and-sour mix on hand and you don't want to use freshly-squeezed juice.
The amaretto sour and margarita belong to a family of cocktails called the sours. Sours are made with liquor, lemon or lime juice and a sweetening agent such as sugar, simple syrup or grenadine syrup. While you can make your own sour mix with sugar, water, freshly squeezed lemon juice and/or freshly squeezed lime juice, many people prefer the ease of a commercial sour mix.
Margarita mix is only one variety of commercially available sour mix. Other versions include sweet-and-sour, Collins and lemon-lime mix. Margarita mix is nothing more than sweet-and-sour mix with the addition of blue food coloring and, usually, a hint of lime flavoring. Since amaretto sours are normally made with sweet-and-sour mix, you can make them with margarita mix if you don't mind a slight blue or green tint in your cocktail. Used in proper proportion to amaretto, the lime flavor of the mix will not overwhelm the almond flavor of the liquor.
Some bartenders add bourbon to an amaretto sour to cut the sweetness. If you are using a powdered margarita mix, substitute orange juice for the water called for in the powder's mixing instructions to balance the lime and complement the almond flavor.
Most commercially available drink mixes contain preservatives, but they can spoil if you don't store them properly. Keep powdered and unopened liquid mixes in a cool, dry cabinet, and refrigerate liquid mixes after opening. Discard any margarita mix that appears discolored.