Preheat the oven
to 375°F/190°C/gas 5. Line two baking sheets with
parchment paper. Sift the flour, cornstarch, and
salt into a medium bowl.
Use a whisk to beat the
eggs, superfine sugar, and orange zest in a double
boiler over barely simmering water until pale and
very thick.
Transfer to a medium bowl. Use a
large rubber spatula to fold in the dry
ingredients. Fit a pastry bag with a 1/2-inch
(1-cm) plain tip.
Fill the pastry bag, twist the
opening tightly closed, and squeeze out 3-inch (8-cm)
lines, spacing 2 inches (5 cm) apart on the prepared
cookie sheets.
Sprinkle with the sugar crystals. Bake for 8-10 minutes, or until just golden.
Cool
the cookies on the cookie sheets for 5 minutes. Transfer to racks and let cool completely.