Candy Apples

Line a baking sheet with parchment paper.
Wash and dry apples. Make sure apples are completely dry, then chill in refrigerator.
Remove stems and insert pop sticks into stem end of apple.
In a deep saucepan, combine sugar, cream of tartar, salt, and 1 cup of water. Add enough food coloring to get desired color. Cook over medium heat, stirring until sugar is dissolved.  Increase heat to medium-high and bring to a full rolling boil without stirring for 8 to 9 minutes. (On a candy thermometer, syrup registers 290ºF.) A small amount of syrup dropped into cold water should form hard threads. 
Remove from heat and immediately dip apples. Twirl to cover evenly, holding apple over pan to catch drips. Place, stick up, onto prepared baking sheet and allow to harden for ten minutes.
Serve immediately or refrigerate and eat within two days.