3. For the croutons: Put flour, salt, and egg into a medium bowl; mix to form a dough. Transfer to a lightly floured surface, divide into 4 pieces, and shape into 4 long 1⁄4"-wide ropes. Cut each rope crosswise into 1⁄4" pieces. (Sprinkle with a little flour to keep from sticking.) Reheat reserved oil in skillet over medium heat. Working in batches, fry dough pieces, turning often, until golden brown, about 1 1⁄2 minutes. Transfer croutons to a paper towel-lined plate and let cool.