Mix together flour, salt and sugar. In food processor or with pastry knives cut in butter until mixture has a cornmeal-like consistency. Whisk together egg and vanilla and mix until the dough forms a ball, then kneed until a smooth consistency develops.
Arrange 4 dozen ungreased small (1 1/2") tartlet tins on a cookie sheet.
With 1 tsp portions, roll dough into small balls and press evenly into tins. Bake tartlets for 12-15 minutes or until golden brown. Repeat process with remaining dough. Dough can be refrigerated up to 1 week or frozen up to a month. Restore to room temperature before working.