4½ cups icing sugar
1 cup almond pieces, coarsely ground
½ cup all purpose flour
1 cup unsalted pistachios, finely chopped
¾ cup egg whites (about 6 large)
¼ tsp corn starch
12 oz semisweet chocolate, for dipping
Preheat oven to 400°F. Line baking sheets with parchment paper. In a large bowl, blend together sugar and almonds until well blended. Add flour; blend until uniform. Add pistachios; blend well.
Using an electric mixer, beat egg whites and ¼ tsp corn starch in another large bowl until stiff but not dry. Fold nut mixture into whites in 4 additions (batter will be thick).
Spoon batter by generous tbsp onto prepared sheets, spacing mounds 1½ inches apart. Bake cookies until dry and cracked on top, about 10 minutes. Slide parchment with cookies onto another surface to cool.
Dip one half of the macaroon in melted chocolate, if desired.
(Can be made 3 days ahead. Store between sheets of waxed paper. These freeze well).