Preheat the oven
to 350°F/180°C/gas 4. Butter four cookie sheets. Butter two rolling pins.
Process the pecans and
sugar in a food processor or blender until finely
ground. Transfer to a large bowl and stir in the
flour, butter, egg whites, vanilla, and salt.
Drop
teaspoons of the batter 3 inches (8 cm) apart onto
the prepared cookie sheets. Do not place more than
five cookies on one sheet.
Spread the mixture out
into thin circles. Bake, one sheet at a time, for
8-10 minutes, or until just golden at the edges.
Use a spatula to lift each cookie off the sheet.
Working quickly, drape it over a rolling pin to give
it a rounded finish. Let cool completely.