Grind the almonds with half of the confectioners' sugar in your food processor, stopping to break up any caking as needed, until finely ground but not at all oily. Sift through a medium sieve. Grind the almonds that don't pass through the sieve with the remaining confectioners' sugar until reduced to a fine powder. Transfer all of the almond and sugar powder to a bowl, break up any caking with your fingertips, and mix thoroughly.
Recipe from "The French Cookie Book", by Bruce Healy with Paul Bugat