Position racks in the center and top third of the oven and heat to 325°F. Line two baking sheets with parchment paper.
Melt the chocolate in the top part of a double boiler over barely simmering water or in a microwave oven. Cool until tepid.
Process the almonds and ⅔cup of the confectioners’ sugar in a food processor fitted with the metal blade until the almonds are very finely chopped, almost a powder. Beat the egg whites with a handheld electric mixer until soft peaks form, then gradually beat in the remaining ⅔cup of sugar until stiff, shiny peaks form. Fold in the almond mixture, then the cooled chocolate. Transfer to a pastry bag fitted with a 7/16-inch-wide plain tip, such as Ateco Number 805.
Pipe 1½-inch-wide mounds of the batter, about 1 inch apart, on the sheets. Bake until the edges are firm and the macaroons lift easily from the paper, about 30 minutes (see Note). Cool completely on the sheets.