In a medium bowl, stir together the flour, salt, and sugar. Add the egg, butter and vanilla, mix until dough becomes stiff. Stir in the sherry 1 tablespoon at a time until dough is workable and smooth. Cover and refrigerate for about 2 hours.
On a lightly floured surface, roll the dough out to .25cm thickness. Cut into long narrow strips, and tie into loose knots, do not pull tight. Heat cooking oil to 190 degrees C (375 degrees F). Oil should be about 4-5cm deep. Fry ties in hot oil for about 2 minutes, until they puff up and turn golden brown. Drain on a brown paper bag or on paper towels. Dust with icing sugar while still warm.