1. Write or print out custom fortunes on strips of white paper about 3 inches long by 1/2 inch wide.
2. Preheat the oven to 400F and grease two cookie sheets.
3. Beat the egg white and vanilla until foamy. In a separate bowl, combine the flour, salt, and sugar and stir gently into the egg white mixture to form the batter.
4. Drop batter by teaspoonfuls onto the first cookie sheet, careful to make the shapes as round as possible. Leave at least 3 inches in between cookies and bake only a few at a time (they must be hot while shaping them).
5. Put the cookie sheet into the oven and bake until lightly golden, about 5 minutes. As the first batch is baking, prepare the next cookie sheet.
6. Remove the first cookie sheet from the oven and immediately lift one of the cookies with a spatula and turn upside down onto a wooden board. Place the fortune in the middle of the cookie and fold the cookie in half. Next, place the folded edge across the rim of a cup and pull the pointed edges down, one on the inside of the cup and one on the outside.
7. Place the cookies in small paper cups or in an egg carton so that they hold their shape until cool.