I make my own nut powders all the time IN THE FOOD PROCESSOR! For almond
powder, you'll need equal amounts of blanched almonds and confectioners sugar
(I make batches of 6 ounces each, nuts and sugar). Grind the nuts with half
the sugar in the food processor, scraping the sides occasionally and breaking
up any caking. Process JUST until the nuts are finely ground - do not let the
mixture get oily. Sift through a medium sieve. Grind the nuts that don't pass
through the sieve with the remaining sugar until the nuts have been reduced to
a fine powder. Transfer all the nut and sugar powder to a bowl, break up any
caking with your fingertips, and mix thoroughly.