1. Stir together the sugar, cinnamon, cream of tartar and boiling water in a small saucepan. Cook over medium heat, stirring constantly, until the mixture comes to boiling; continue to boil until the mixture registers 240 degrees F (soft-ball stage) on a candy thermometer, about 8 minutes total.
2. Remove saucepan from heat. Stir in pecans. Let cool a few minutes. Add vanilla and stir until pecans are evenly coated. Pour pecans onto sheet of waxed paper. Separate the nuts with 2 forks. Let cool.