Amaretto is a sweet, almond-flavored Italian liqueur made from almond pits. The most well-known brand is Amaretto Disaronno. In addition to being served as a drink, it can be used over ice cream, as a flavoring in baked goods, as well as other desserts.
Amoretti di Serroni is an amaretto-flavored macaroon very famous in Italy. The cookies are crisp and crunchy with a distinctive bitter-almond flavor. If you need a substitution for these cookies in a recipe, the best alternative would be to use some almond extract, or Amoretto, if you have it. Neither will reproduce the texture if that is important but will give you that nice almond flavor. Alternately you could use almond biscotti if you need another cookie and not just flavor.
For an alternative with alcohol and a different flavor variation, try substituting equal amounts of: