Combine the first 6 ingredients in the top of a double boiler. Cook over simmering water until chocolate melts (about 2 minutes), stirring constantly. Spoon mixture into a shallow dish. Let stand at room temperature 6 hours or up to overnight.
Scoop about 1 tablespoon chocolate mixture with a spoon. Dredge in nuts; roll into a ball. Repeat procedure with remaining chocolate mixture and nuts.